North America

oduc

in the rocks in much the same manner that the historian searches the papyri or the monuments of Egypt to discover what changes in the affairs of men have occurred since the days of the Pharaohs. The changes referred to are not essentially different from those now in progress, but in reality the two are parts of a single series. For a very long time there have been continents and oceans, lakes and rivers, and the land has been diversified by mountains and hills, plains and valleys, in the same general way as at the present time. When once the idea is grasped that we are living in a geological age, and that there is no break between the present and the past, it is evide

H OF THE

there have been numerous islands, and as a large portion of the records of past changes which have been presented were formed in the ocean, the results are complex. But in North America there has been a comparatively steady growth from one main continental centre or nucleus, and the records of the principal changes

sion of the margin of the land by waves and currents and the deposition of material brought from the land by streams, together with the spits, bars, and embankments made

own by various geologists, the outlines of the present continents and ocean-basins had their major features determined at a very early stage in the history of the earth, and at a time preceding the existence of the oldest known sedimentary rocks. At the close of the Archean, the earliest geological era now recognised, and,

ism of sedimentary beds. Penetrating and intimately intermingled with these greatly altered rocks, some of them perhaps metamorphosed lavas and allied terranes, are many rocks that were forced upward from deep

nd the continent was enlarged. The outline of the land as it existed previous to the upheaval which exposed this portion of the ocean's bottom would be defined by the landward margin of the material deposited. The exposed sediments would be coarsest near the former coast-line and become finer and finer seaward from it, and the fossils contained in the consolidated sands and clays would also supply evidence bearing on the origin of the rocks. I

sitions they occupy on the geological time-scale are shown a few

rth's crust beneath the northeastern part of the region now occupied by the United States, portions of the sediments deposited previous to the close of the Silurian were upraised and important additions made to the extent of the land southward from the Archean area of Canada. This "Appalachian peninsula" would be conspicuous in a map representing the outline of the continent at the close of the Silurian. The eastern margin of the growing continent was then well to th

in their prime. The time indicated is at the close of the Paleozoic era, and after the great coal-fields extending from Pennsylvania southward to Alabama and westward

The conspicuous features in the geography are the submerged Atlantic and Gulf borders, and the presence of a broad belt of ocean water in the continental

ward and a wide area about the Gulf of Mexico, were submerged and had deep layers of sediment deposited on them. During the Tertiary, bodies of fresh water became for the first time a conspicuous feature on the land, and large lakes and broad silt-d

the growth of the Nor

. 3

. 3

. 3

and greater diversity in its relief, due principally to the upraising o

not now of sufficient elevation or ruggedness to be termed mountainous, it shows in the nature and structure of its rocks that deep erosion has taken place. The inference is that truly great

e Appalachian region at the close of the Paleozoic era. The Park and Stony Mountains were upraised at the close of the Mesozoic era, and later came the Sierra Nevada and Cascades, followed by the Coast Ranges. Youngest of all, and in part for that rea

to the eastward of the Sierra Nevada. The majestic cones of the northwestern portion of the United States, of which Mounts Shasta, Hood, Adams, Rainier, Baker, etc., are the most glorious, are of Tertiary or later age. The same is true, so far as known, of the still more lofty volca

HICH THE CONTI

he cooling and crystallizing of formerly molten magmas; second, those deposited by water; and third, those which previously belonged to either of th

y might be termed from analogy with systems of bio

s, such as the

uch as sandstone, shale

such as gneiss, schi

e theoretically at least, and in a general way, the rocks of these three great classes came into exis

ading geolog

mage to

by streams, the solvent power of water, etc., and the fragments thus produced are removed principally through the action of flowing water and deposited. Resulting from this general process of rock decay and disintegration, combined with transportation and deposition, there result me

edimentary rocks have been in process of formation, and in this way the growth of

maximum in the Appalachian region, where a depth of some 40,000 feet has been measured. Throughout the continental basin their depth is in general from 3,000 to 4,000 feet. In the Pacific mountains their thickness embraces tens of thousands of feet, and the same is true

th the sea. In certain broad regions, sedimentary beds which formerly existed have been removed by erosion; in other extensive areas they are covered by volcanic ro

ion above another, in regions where but moderate disturbances in position have occurred. Many of the stratified rocks contain fossils-that is, records of the life of the time they were deposited

ntained in them, a composite geological column has been constructed which shows the relative age of all known formations. The larger divisions

g at the bottom. There is some lack of uniformity among American geologists as to certain of the terms used, more especially in the lower portion of the column, and

groups and systems and the eras and periods, have for the most part been adopted from Europea

he Geological Hist

e. ? Grou

le. ? Er

ince the appearance of life. Time of Mammals. T

c. Plei

eptiles.

of Cy

c. Cret

of Acrogens (Ferns, club-

c. Carbo

Fishes.

uri

luscs and C

Alg?. Or

bri

. Algo

As yet unknown pre-

dawn of life. Azoic. Arc

ric Soli

en E

ous

ssion of sedimentary beds, igneous and metamorphic rocks

the main Archean nucleus of the continent, but rocks of the same age and same general character occur in several of the mountain systems of both the Atlantic and Pacific cordilleras, and underlie the sedimentary beds throughout a large part of the Continental basin. The Archean system was named by J. D. Dana, and divided into two portions, namely, the Laurentian below and the Huronian above. More recent studies, especially by C. R. Van Hise, have shown the necessity of removing from the

erives its name from a tribe of Indians that inhabited the region about the shores of Lake Superior, where it is well developed. The Algonkian terranes are exposed in the Grand Ca?on of the Colorado, in the Wasatch and Uintah Mountains, the Black Hills of Dakota, about the southern shore of Lake Superior, and in many parts of eastern Canada, as well as in several ot

n beneath subsequent deposits. The most interesting results derived from the study of the Cambrian, carried on especially by C. D. Walcott, pertain to its life records. With the exception of a few obscure alg?, all the fossils thus far discovered are marine invertebrates. As regards rank in the zoological scale, certain molluscan r

shallower portions near land and over its surface, contains alg?, mostly, we presume, of small size, in fact microscopic, and soft tissued. The animal life subsisting primarily on the alg? are all invertebrates, and nearly all of them, excepting the crustac

fauna stands at least half-way, and some students of the ancient history of the earth place it as far as nine-tenths of the way, up the life column-that is, the time from the first appearance of life on the earth to the beginning of the Cambrian was at least as long and possibly

t contribution to the world's knowledge, from the study of the American records, include the discovery of a large number of fishes, or fish-like forms, some of them of gigantic size, in the Devonian and Carboniferous r

as densely clothed with forests consisting of flowerless plants such as ferns and c

ich the coal-beds of Pennsylvania, Ohio, Nova Scotia, etc., were accumulated have been made by

cycads being especially numerous, and of our ordinary broad-leaved trees, such as the oak, willow, sassafras, etc., and by

es of J. S. Newberry, Leo Lesquereux, W. M. Fontaine, L. F. Ward, F. H. Knowlton, and others. These same students o

d stood 10 to 14 feet high where the massive hind limbs joined the body. Their thigh-bones in certain instances measured over 6 feet in length. Some of these monsters, it is estimated, weighed at least 10 tons. These, the hugest of all land animals, were vegetable feeders. Others, of less size, although still gigantic and more active, were carnivorous. Some of the old lizard-like forms which left their footprints in great abundance in the sands now hardened into sandstone in the Connecticut Valley and New Jersey walked on their hind feet, after the

f reptiles, have been discovered in the Mesozoic rocks of Kansas. Important additions to our knowledge of these strange creatures, which furnish much instructive data in reference to the development of the higher from th

ountain region, a great number of skeletons of truly remarkable mammals, differing widely from anything now living, have been discovered by Joseph Leidy, O. C. Marsh, E. D. Cope, H. F. Osborn, and others. The profound interest attached to this fauna, and the bearings it has on the study of the geog

ut the Pleistocene period and were then probably more numerous and of even larger size than during the preceding Tertiary period. During the Pleis

ed, but important contributions to knowledge concerning the brute mammals, an

astodon and elephant, megatherium, megalonyx, mylodon, a large horse, a great bison, an elk much exceeding the living species in size, a giant beaver, and many others remarkable for their large

rhaps in late Tertiary time, the continent in large part at least was more elevated than now and the energetic streams of the mountainous portions eroded deep ca?ons. To this Sierran epoch, as it is t

ice-sheet now covering Greenland to expand from at least three centres, termed the Labradorean, Keewatin, and Cordilleran, in what is now Canada. During this time of great ice accumulation and of glacial advance and retreat, or the Glacial epoch, as it

istocene gla

l occupied by ice. The broken blue lines on the Atlantic and Pacific coasts show approximately the seaward extension of the Pleistocene ice-sheets. The detached areas of glaciation in the western portion of the United S

mage to

arlier advance from the Keewatin centre extended to the Missouri River in Missouri. There is evidence of a succession of advances and retreats of the ice forming

within recent years energetically carried forward by a large number of earnest workers. The stage of advance reached in this branch of geology w

ks, has been made known by the combined studies of a large number of investigators, but the great task has been carried on mainly under the auspices of various national and State survey

lten condition. The starting-point of the study of the rocks composing the earth should be, therefore, the primitive crust cooled from fusion. In addition to this there have been throughout history geologic migrations of molten matter from deep within the ear

certain branches of the subject, as the nature of intrusions and the changes which occur in the cooli

tions in the same connection, some of them in an advanced stage of erosion and now revealing only the dikes and necks of resistant rock that cooled and hardened well below the surface, occur widely throughout the southwest portion of the United States. The still recognisable volcanic mountains of the continent, with the exception of those of the Caribbees, are confined to its western half, and with the exception of certain almost perfect craters in eastern New Mexico are all within the Pacific mountains. A great belt of volcanoes, including a large number of both active and extinct examples, extends from Panama to the Aleutian Islands, a distance of some 7,000 miles, and

nent the time since the last eruptions has been so great that all evidence in the relief of the land of the former presence of volcanic mountains has been obliterated. Erosion has cut deeply into the rocks on which the ancient volcanoes stood, and revealed in some instances the dikes occupying the fissures which supplied them. A large number of dikes of igneous rock occur in the Atlantic coast region from Prince Edward Island southward to Alabama and Georgia, and vast lava-flows of ancient date are still preser

ominates. An exception occurs in the case of the Mono craters near Mono Lake, California, which in recent time extruded

er the land. More or less extensive sheets of this material, in many instances interstratified with sedimentary beds, and especially with the strata laid down in Tertiary lakes, or separating lava-flows, occur widely throughout the Pacific mountains. Dust showers

tal layers of basalt, a thickness of 4,000 feet is revealed, although the stream has not as yet cut through the formation, and in Stein Mountain, Oregon, a similar series of lava-sheets over 5,000 feet thick has been measured. The Columbia River lava was spread over the surface of a deeply eroded land in a series of vast overflows of molten material. The liquid rock covered the broad plains and extended into the valleys in the adjacent mountains, giving them level floors of basalt. Mountain spurs became capes and headlands and outstand

highly varied process. As geologists have discovered, particularly in deeply eroded regions, by no means all of the fissures which permit of the forcing upw

, are of common occurrence and are frequently abundant in deeply eroded regions. They occur particularly in mountains of upheaval, thus demonstrating the fact that to a large extent the fissure which became injected with molten magmas and perhaps gave origin to volcanoes, are due to movements in the rocks composing the earth's crust. The force which causes molten rock to rise in such fissures also tends to prolong and enl

his nature is furnished by the palisade trap-sheet in New Jersey and New York, which has a maximum thickness of about 1,000 feet, and is fully 100 miles in length from north to south. The portion which remains is but a remnant and is seldom over 2 or 3 miles wide. This sheet in common with its associated sandstones and

s to a great height. Intrusions of this nature are sometimes expanded in their upper portions into a more or less mushroom shape, and from their fancied resemblance to cisterns of once molten rock within older terranes have been termed laccoliths. The typical examples are furnished by the Henry Mountains in southern Utah, described by G. K. Gilbert. Other similar intrusions in Colorado have

e form, similar to the conduit of a volcano, but without reaching the surface, the unexpanded or but slightly enlar

a genetic connection between intrusions on the one hand and volcanic and fissure eruptions on the other. If fissures lead from portions of the earth's crust sufficiently deep to permit the rocks to become plastic or fused on account of the relief of pressure due to the opening of the fissure, the magma may be forced to the surface, becoming more and more plastic or more perfectly fluid as the weight upon it decreased, and volcanic ph

th's crust, which elevate domes, perhaps 200 or 300 miles or more in their various horizontal diameters. The great areas occupied by intrusive granite, as the one from which the Bitter Root Mountains in Idaho have been sculptured, are of this nature. These "regional intrusions," as they may be termed, elevate m

f an alteration in the colour, texture, hardness, mineral and chemical composition, etc., of the rocks affected, and may be manifest throughout a thickness of but a few feet, or perhaps only a few inches, but near large intrusions is apt to be traceable for scores or hundreds of feet. In the case of intense contact metamorphism, the altered rock assumes a new form, and may exhibit a cryst

sion from a previous condition, during which they were either sedimentary beds or cooled and crystallized igneous magma. This conclusion has been verified in numerous instances by tracing the thoroughly altered rocks to regions where the change has been less intense and finally to where they pass by insensible gradations into easily recognisable sedimentary or igneous terranes. Common examples of metamorphic rocks are mica, schist, gneiss, statuary marble, certain granites, etc. These ro

of the material while under pressure. In short, rocks are altered by heat, especially if water is present in them, by motion, and by chemical changes produced by percolating waters, and perhaps in still other ways. The degree of heat required is not definitely known, and probably varies according to the nature of the rocks, the presence or absence of water, etc., but is certainly less than that necessary to produce fusion, and

heastern Canada, in Labrador and Newfoundland, in the New England States, and thence southward along the eastern side of the Appalachians. Other exte

ion of certain areas where igneous rocks occur, is formed of metamorphosed terranes. So generally is this true, that it is safe to say that if a boring is begun at any locality on the continent where sedimentary beds occur, and is continued downward until the sedimentary rocks are passe

y age may be altered in the several ways mentioned above, and the resulting gneisses, schists, etc., be indistinguishable from those of the Archean. In fact, some of th

of action of the forces which upheave the rocks so as to form land areas, and also of the movements in the rocks which produce fractures and lead to the origin of volcanoes. In a simi

s intrusions similar to those noted above in connection with sedimentary rocks. As the stratification so marked in sedimentary beds is lacking in metamorphosed rocks, it is not to be expected that intrusions will take the form of sheets, laccoliths, etc., but rather appear as dikes with perhaps irregular branches. As the same region may experience two or more periods of metamorphism, it is evident that great complexities may arise, as, for example, when a metam

ocks have been formed at the surface from the débris of either igneous, metamorphic, or previously formed sedimentary beds; and that metamorphic rocks have been produced within the earth's outer crust by the alteration of either igneous or sedimentary rocks. When the heat which produced certain phases of met

s outer crust is necessary to the understanding of the conditions observed in the basal portion of the geological column, as it is termed, in which the age and order of succession of the sedimentary rocks is indicated. In certain localities, for example, the Cambrian rocks rest unconformably on a surface of metamorphic and igneous rocks-that is, the Basement Complex was raised above sea-level, eroded and subsequently depressed before the Cambrian sediments were laid upon it. In other localities the Cambrian rocks pass indefinitely into metamorphosed terranes beneath, which means that metamorphism invaded the series after the deposition of the Cambrian, and the characteristics of its junction with older rocks was obliterated. Similar relations may evidently be discovered at any horizon in the geological column. Obviously the chances of a system of stratified rocks becoming metamorphosed or of being removed by erosion, are greater the nearer their position to the base of the sedimentary series; in a similar way

TION OF MINER

man, as, for example, building stones, coal, iron, petroleum, gold, etc. Only a glance can here be given at the c

n minerals and ores will be developed or concentrated in one class of rocks and not in the others.

aining the metallic element, etc., which are of economic importance, these are widely disseminated, and in nearly all cases in chemical combinations, as the minor ingredients of siliceous minerals. Although the igneous rocks sometimes contain valuable ores, they are in many, if not all instances, due to secondary enrichment and

d by streams and redeposited. In this process an assorting in reference to size, specific gravity, etc., takes place, and certain substances, as sand, for instance, is accumulated in one locality, and certain other substances, as clay, deposited in another locality. During this process gold, platinum, etc., owing to their high specific gravity, may be concentrated in stream channels. The accumulat

te from water and deposit it in their shells or skeletons. The part played by plants in this same connection is shown by the way in which they eliminate carbon dioxide from the air or fro

ether largely by water and crystallized to form mineral species. In order to simplify this brief discussion as

ital agencies operate at the surface of the lithosphere, although organic products, principally certain acids, descend into the earth in solution in water and play an important part in

nly through the aid of flowing water, are in general most potent in humid regions and where the land is high above sea-level. Vital agencies depend lar

fusion, for example, permitting of the intimate mingling or recombination of substances, previously segregated, although during the dying s

fferent, and hence in a marked way the stones, ores, fuels, gems, etc., to be expected in each of the three classes of rocks, respectively, are distinct. Certain exceptions to this broad conclusion, however

segregation of metallic minerals or ores. Although igneous rocks do contain gold, silver, copper, etc., and a large variety of the rarer metals, they are widely disseminated. As is well known, however, igneous rocks are in some instances of value for the metallic mineral, gems, and ores associated with them, but in the great majority of instances at least, and as a rule, these minerals and

been altered to serpentine, which on account of its pleasing green colour and the ease with which it can be cut and polished furnishes a stone valuable for interior uses. It is also employed, usually with a rough surface, in the construction of exterior walls of dwellings,

s, including the Treadwell mine, Alaska; opal, which is mined on a small scale in Idaho and Washington. In practically all these instances, and numerous others that might be enumerate

f sandstone, shale, etc., and of organically concentrated material, such as shells and corals, which form limestones. The deposits originating in these ways furnish excellent building stones, the principal classes being sandstones and lim

e Adirondack hills of New York. They are usually red or reddish-brown rocks, and their pleasing colours, durabilit

of the interior portions of the United States. Extensive deposits of Mesozoic and Cenozoic sandstones occur throughout the Pacific mountains, and afford a practically unlimited supply of good building material, which as yet has been but little utilized. The colours of sandstones vary from bright red through brown-yellow to gray, and in some cases are nearly white, depending largely on the condition of the iron present. The red rocks are dyed w

ing stones used for architectural and monumental purposes, as foundry sand in making moulds for casting, and many other ways. Seaward from where sand is being deposited we find in the present oceans that as a rule fine bluish or greenish mud occurs, and still farther seaward, except where coral-polyps thrive, usually at a distance of 100 miles or more from land, the bottom is composed of calcareous mud or ooze. The sand and mud are derived from the land, and if cons

ndicated. From this mode of origin it may be truthfully inferred that limestone may have been formed during any age since organisms having the power of secreting calcium carbonate e

tly consolidated shells of living species of molluscs, are used in the construction of buildings. Gray limestones susceptible of a good polish occur in Ohio and neighbouring States and are utilized to some extent for columns and interior finish of buildings, but in the main the stones of this natu

, and converted into crystalline marble. Commercially, however, all limestone,

., are precipitated, and in caverns where stalactites and stalagmites are formed. Stalagmite sheets are sometimes composed of variegated, laminated layers, and when po

ly through the vital action of certain alg? and deposited as a fine white ooze. Thousands of deposits of this nature, varying in extent up to several hundred acres, and having a depth of from a few feet to 40 and even 60 or more feet, occur in the portion of the continent covered with glacial drift, and especially in the States from New England to Minnesota. The re

es of economic value is illustrated by the manner in which coa

n swamps, a slow change takes place and peat is formed. The essential conditions for the accumulation of vegetable matter have been present on the earth ever since a land flora existed, and coal-beds occur at many different horizons. The earliest date at which land plants seem to have been sufficiently abundant to furnish material

the distribution of c

t but little known coal-bearing formations of Asia, and are distributed in temperate latitudes, from tide-water on the A

nd westward to beyond the Mississippi. A detached coal-basin containing some 6,700 square miles, but a small part of which is productive, however, occurs in the central part of southern Michigan. Small coal-fields in Virginia and North Carolina, the first to be worke

lignites, but in many instances of high grade and serviceable for steam coal, are mostly of Cenozoic age (Tertiary) and occur in California, Oregon, Washington

from Louisiana and Florida northward, to the region about the Great Lakes and widely throughout Canada, but

manufacturing gas and coke. The exceptions occur in eastern Pennsylvania and in Rhode Island. These are considered as metamorphosed coals, although in the Pennsylvania region there is no evidence of the

penetrated by dikes and other varieties of intrusions, or have been altered by surface lava-flows. In such situations the coal has lost nearly all i

gin and to have resulted from changes which take place in vegetable and animal tissues when buried and in most cases subjected to heavy pressure. A large part of the hydrocarbons referred to is thought to have been derived from animal organisms, an opinion which is sustained in an important manner by the fact that large stores of both petroleum and rock-gas have been discovered in rocks which were laid down bef

favourable conditions for the

imals are buried in the rocks, but the petroleum, gas, etc., generated escape at the surface and pass into the air and are again widely disseminated, unless conditions are present which lead to their accumulation. The conditions favouring the natural storage of the substances referred to are cavities, or more usually porous beds, such as sandstone, beneath impervious beds, such as clay or shale. The conditions are still more favourable when lateral as well as vertical escape is cut off, as, for example, when

ork, Ontario, Ohio, and Indiana. The Devonian rocks of Pennsylvania, New York, Ontario, etc., also yield large supplies of both oil and gas. Mesozoic rocks of Colorado, Wyoming, etc., are also rich in the concentrated hydrocarbon referred to, and on the Pacific coast, particularly in California, rocks of Cenozoic age are highly productive. Petroleum and gas may occur also in rocks more recent than the Cenozoic, but owing to the absence of reservoirs,

o, yielded over 17,000,000 cubic feet per day. In 1890 the average daily flow of the Indiana gas-wells was

, under the most plausible explanation thus far offered, from the concentration by evaporation of fluid hydrocarbons such as petroleum. The evaporation, particularly of heavy petroleum, leads to the formation of

hamite, occurs in fissures in rock of the same age, near a rich oil-pool in West Virginia. Other similar deposits, but usually wax-like and dull, are found in Utah and neighbouring States. Asp

y distributed throughout the portions of North America where the surface is composed o

nozoic and more recent terranes. Beds of diatomaceous earth reported to be 40 feet thick and of wide extent have been found near Richmond, Virginia, and similar deposits occur at several localities in Oregon, California, etc. The uses of

ccumulation to chemical agencies acting at the surface of the

he salt in this the Salina formation there are many beds of gypsum. In rocks of Carboniferous age in Michigan, other extensive beds of salt and gypsum have been discovered. In Louisiana, Texas, Utah, and other States, salt and gypsum occur in Mesozoic and Cenozoic rocks. One of the most remarkable of these deposits is beneath small islands in the Gulf of Mexico off the Louisiana coast. On Jeffer

uch, for example, as sodium sulphate, of which large beds occur in the desiccated lake basins of the arid r

us new combinations. When organic acids are present, and especially carbon dioxide, ferrous carbonate is formed, which is quite soluble, and is taken into solution by percolating water, some of which emerges as springs, and joins the surface run-off, which may also take up ferrous carbonate in solution. One of the most common methods by which iron ore is accumulated is when water carrying ferrous carbonate in solution forms swamps and lakes, and in many instances as the water is exposed to the air and aided by evaporation it parts with a portion of its carbon dioxide, and the hydrated sesquioxid

ed outcrops, owing to the removal of the more soluble ingredients and the leaving of the less soluble oxidized iron, have a yellow, brown, or red colour, and in some instances this process of concentration has produced workable iron ore. Limonite and earthy hematites occur widely throughout the Appalachian region, in central New York, and westward to the Mississippi Valley. One of the most productive formations is the Clinton, a division of the Silurian

band ore and kidney ore, occur. The former is present as regular strata and the latter in oval concretionary masses. These ores, although not as rich in iron and less pure than certain other

to hematite and magnetite. The richest iron ores of North America are of this nature, and will be referr

of potash, which makes them valuable fertilizers. In this instance the concentration took place on the floor of the sea, through the action of decomposing organic matter, and the potash-bearing mineral of the greensand, namely, glauconite, was deposited in the

hatic nodules, which have been derived from organic matter. The guano deposits of the low arid islands

which occur widely throughout the portions of North America where the surface is composed of stratified rock,

chanical separation of the heavier from the lighter material takes place and all but the very finest of the gold is concentrate

e considered to have been at one time widely distributed in the adjacent sedimentary rocks, mainly limestone, and to have been taken in solution by percolating waters and carried to cavities where they were precipitated, together with various other mineral substances, such as calcium carbonate or calcite, barium sulphate or barite, carbonate of calcium and magnesium or dolomite, etc. The minerals containing lead are principally galenite or lead sulphate, cerussite or lead carbonate; while the zinc is contained in the minerals, sphalerite or zinc sulphide, calamine or zinc silicate, smithsonite or zinc carbonate, e

ound in cavities in Cretaceous limestone; at Leadville and Aspen, Colorado; Big and Little Cottonwood ca?ons, and the Horn silver-mine, Utah, where the principal country rock is Carboniferous limestone; the Eureka district,

substances. Veins are thus formed, which are many times banded-that is, result from the filling of fissures by the successive deposition of minerals of various kinds on their walls, each different layer of minerals indicating a change in conditions. Fissures filled in this manner from below, as denudation progresses, become exposed at the surface and reconcentration through the influence of disintegration and decay, and of solution and redeposition by desce

ove or below, as in the former direction metamorphism merges by gradations into alteration produced by the descent of surface water, and in the latter direction as heat increases passes again, as we imagine, by insensible and irregular gradations into a region where the rocks are so highly heated that diffusion rather than concentration results. Whether the rocks below the zone of metamorphism are fused or not depends on pressure. They are probably solid, but in a potentially plastic con

ely disseminated through rocks is, under the action of percolating, heated water, brought together and the regeneration and crystallization of a large variety of ores and minerals result. The birthp

d a still further concentration, principally in fissures and other cavities, is necessary before they can be of value to man. This secondary concentration is much the same as in the case o

bodies, frequently of great size, in some instances furnish evidence of having been originally lenticular masses of bog-iron ore, or ferric carbonate, associated with sedimentary beds, and originally concentrated, as already mentioned, at the surface through the action of water charged with carbon dioxide, but principally on account of the influence of heat have been changed to a higher degree of oxidation and

that of the Lake Superior region, has resulted from the alteration of ferrous carbonate

y age, and as rocks of any age may be metamorphosed, it follows that hematite and magneti

ts previously contained organic matter. The white marbles so extensively utilized in Georgia, Vermont, etc., are of this

happened adjacent to dikes or intruded sheets of igneous rock in the Richmond coal-field, Virginia, in New Mexico, Washington, etc. When the heat is somewhat more intense, the coal is changed to what is termed graphitic

such as the garnets, tourmaline, emerald, sapphire, corundum, etc., which are of economic importance. In a large number of instances the minerals of metamorphic rocks are contained in veins of one class or another, in part resulting from segregation in the rocks themselves while yet in a heated condition, and in part deposited in fissures or other openings as a r

erranes of North America, other than building stones and the previously concentrated depos

l for electric wires, fireproofing, and also used as a lubricant, etc., occurs in large quantities in the metamorphic rocks of New Hampshire and Ottawa, and les

and when ground, employed as an adulterant of soap, paper, rubber, and as a lubricant, etc., occurs widely in the metamorphic terranes on the eastern side of the Appalach

cellent insulator, and largely used in the manufacture of fireproof paper, cloth, etc., occurs in connec

., and also as "sand-paper" in working wood, occurs in commercial quantities, largely in crystalline limestone, at Chester, Mass., in Georgia, North Carolina, and several other localities. Although corundum is next to the diamond in hardness,

rth America but thus far in minor quantities, and as a rule of inferior qua

ted with limestone in the metamorphic rocks of Quebec and Ontario in the form of veins, beds, and irregular po

etc., it occurs in flakes and grains, but so far as its occurrence in commercial quantities is concerned its deposition has for the most part been secondary, and the metal, usually in association with quartz, is found in veins, lodes, contact deposits, etc., and owes its concentration to chemical agencies not well understood, acting in connection with percolating water. That this general statement is correct is clearly shown by the fact that gold occurs in crystals, flakes, grains, etc., most frequently in quartz and iron pyrites, which, as can be shown in a number o

usly quite largely exploited, of the Atlantic mountain region from Georgia to eastern Canada. The mines of California are also largely in schistose rocks, as ar

phic rocks, there are frequently found grains of platinum. The annual product

waters, and in part redeposited in higher terranes. Erosion has since carried off the rocks which were mineral-charged and laid bare the depleted terranes beneath. This hypothetical explanation of the general poverty of the Archean rocks is coupled with another consideration, namely, that the younger metamorphic terranes, where they have been elevated, as in the Pacific mountains, are more broken th

t $7,000,000 annually. The demand for these waters depends largely on the mineral substances they hold in solution, and which in many instances is in process of transference from one l

ERA

the Geological Survey of Mexico contain vast amounts of valuable information. Several of the States of the United States have independent surveys and have published numerous reports. Of journals containing articles of American geology, the more important are: The Journal of Ge

iographies of North

merican Geology, 1732-1891. Published as Bulletin No. 127 of

of the Geological Survey of Canada], 1863-1884. Published

States Geological Survey, 1880 to 1901. Published as Bulletin No.

ology, and Mineralogy for the Years 1892-1900, Inclusive. United States

the geology, the following will be fo

y. Fourth edition. American

United States and Canada. Scientific

revised and partly rewritten by Prof. H. L. Fai

, Rock-Weathering, and Soils. The

Earth's History. D. Appleton