Public domain
[p. 805] [1]
The distribution of the Miocene system (Fig. 541) shows that the geography of the North American continent was much the ime during the Miocene period as during the Eocene, the sea covering no more than narrow borders of the present land. The slight emergence of the coastal borders after the Eocene (or early Oligocene) was followed by a slight submergence of the same regions during the Miocene. In the western interior, wide-spread terrestrial aggradation of all phases continued, but the sites of principal deposition differed somewhat from those of the preceding period.
The Atlantic coast. In its surface distribution, the Miocene sustains the same relation to the Eocene that the latter does to the Cretaceous, though it sometimes overlaps the Eocene, completely concealing it. There is generally a slight unconformity between the Miocene and the Eocene (or Oligocene). Like the other formations of the Coastal Plain, the Miocene beds dip seaward and are concealed by younger beds some distance to landward from the present shore line. The general relations are indicated by Fig. 499. The system originally extended inland far beyond its present border, as shown by numerous outliers.
The Miocene of the Atlantic coast is composed chiefly of unconsolidated sand, clay, and shell marl. In places, diatomaceous earths are found in beds of such thickness (30 or 40 feet) as to be valuable commercially. In New Jersey,[2] the Miocene reaches a [p. 806] thickness of 700 feet, in Maryland,[3] about 400 feet, and in North Carolina it is still thinner.
[p. 807]
The Miocene of the Atlantic coast is generally called the Chesapeake formation. This was formerly regarded as Upper Miocene, the former Lower Miocene being now classed as Oligocene. The fauna of the Chesapeake series has been interpreted to indicate a climate somewhat cooler than that which had preceded.
The Gulf coast. The Miocene of the Gulf coast sustains the same general relations to older formations as that of the Atlantic, except that it is not known to be so generally unconformable on the beds below. Excluding the beds classed as Oligocene, the Miocene of this region has but slight thickness. In Florida, the Miocene limestone has been changed locally to lime phosphate.[4] The alteration appears to have been effected through organic matter, especially the animal excrements accumulated about bird, seal, and perhaps other rookeries. The organic matter furnished the phosphoric acid, which, carried down in solution, changed the carbonate of lime to the phosphate. The phosphate has been extensively used as a fertilizer for soils. The Miocene is represented in Alabama and adjacent stages (the Pascagoula formation) and in Texas (Oakville beds), where both marine and non-marine phases are present. Much of the oil of Texas and Louisiana (Beaumont, Sour Lake, Saratoga, Jennings, etc.) comes from dolomized limestone which overlies Eocene (or Oligocene) clays, and is probably Miocene.[5]
The Pacific coast.[6] At the beginning of the period, the sea encroached upon the Pacific coast, covering considerable areas which were land during the Oligocene time. It flooded the southern part of the central valley of California early in the period, and later the northern part as well. At about the beginning of the period, faulting seems to have affected considerable parts of California, and some of the planes of movement at that time have served as planes of movement until now. This was the time of [p. 808] the first definitely recognized movement along the great earthquake rift of California. Though subsidence was the rule in central and southern California, local fault-blocks seem to have had notable elevation.
The Miocene history of the Pacific coast is divided into two somewhat distinct epochs, the earlier and the later, the separation being marked by diastrophism and vulcanism.
The lowest (Vaqueros) formation of the early Miocene in southern California is largely clastic, but later beds (Monterey) contain a large amount of diatomaceous material, and the diatomaceous beds are an important source of oil.[7] The amount of silicious material ascribed to diatoms is prodigious, and only seems credible when the extraordinary rate of reproduction of diatoms is recalled. It has been estimated that a million individuals might come from one in the course of a month. If this is the fact, it is perhaps not strange that large amounts of silicious material accumulated in places where conditions were favorable for diatoms. Vobanic ash is also a constituent of the Lower Miocene. As implied above, the Miocene is generally unconformable on the Eocene or on ol< Informations.
After the early Miocene, igneous eruptions were extensive in eastern Washington, Oregon, and the Coast ranges of California. South of San Fransisco, this was the time of the last important eruptions in the Coast ranges, though vulcanism continued 1: in Oregon and Washington, and perhaps to some extent in northern California. The igneous eruptions accompanied the Mid-Miocene diastrophism referred to above, which consisted in the readjustment of fault-blocks and folds throughout the Pacific coast region. This readjustment went so far that even high mountains v. developed locally, as shown by the coarseness of the sedime which followed.
After the diastrophism referred to, the extension of th< over present lands on the Pacific coast was greater than at any time since the Eocene. It was not until this time that the northern part of the Central valley of California (Sacramento valley) was [p. 809] submerged. The Upper Miocene beds are therefore more widespread than the Lower. While clastic sediments predominate, diatomaceous earths are still in evidence.
The marine part of the Miocene system attains very notable thickness, the Lower Miocene having a maximum thickness of some 8,000 feet (Vaqueros 3,000, Monterey 5,000) and the Upper Miocene hardly less.
[p. 810]
By the close of the Miocene, the peneplanation of the Klamath and Sierra Nevada mountains seems to have approached completion. Much of the material eroded from these mountains had been deposited in the central valley of northern California, givinJ the thick Miocene beds of that valley.
In western Oregon, Miocene (Empire) beds a few hundred feet thick, containing volcanic ash, rest unconformably on the deformed and eroded Eocene.[8] In British Columbia, there are both elastic and volcanic rocks referred to this period.
The Miocene of the western coast has not the simple structure of the corresponding beds along the Atlantic and Gulf coasts. The strata have been deformed so as to stand at high angles (Fig. 544) in many places, and locally (Mount Diablo range), they have been folded, and the folds overturned so that the Chico (p. 752) and Tejon (p. 781) series overlie the Miocene.[9] The Miocene beds [p. 811] are found in some parts of the Coast Range[10] of California up to elevations of 2,500 feet.
Non-marine deposits. The sea seems not to have overspread the northern part of the central valley of California when it did the southern, and at the north there were deposits of estuarine, lacustrine, and probably sub aerial origin (Ione formation) contemporaneous with the marine beds farther south. They consist of the common sorts of clastic sediments, with some coal, iron, etc.
Along the east side of the central valley of California, auriferous gravels,[11] brought down by streams from the Sierras, were being deposited in the lower courses of the valleys during at least a part of the period. These gravels seem to have been deposited on a surface of slight relief, interpreted as a peneplain.[12] The tilting of this plain toward the end of the Miocene seems to have quickened the upper parts of the streams and caused them to deposit gravel below. The Sierra Mountains are thought to have been at least 4,000 feet lower than now when these gravels were deposited. From some of the gravels of California, thought to be of Miocene age, human relics have been reported,[13] but there seems to be the best of reason for doubting their authenticity.
Non-marine Miocene beds are rather wide-spread in south [p. 812] eastern California and Oregon, reaching great thicknesses (4,000 feet, King) at some points in the vicinity of the 40th parallel. In general, they are made up of sandstones, conglomerates, volcanic debris, infusorial earths, and fresh-water limestones. Other areas of deposition, some of them lakes, existed during the Miocene in Nevada (Esmeralda formation) and Montana (Bozeman formation).
Farther east, on the western part of the Great Plains, the deposition of the White River beds may have continued fog a time after the beginning of the Miocene, as indicated by the fauna of the uppermost beds. Late in the Miocene period. aggradation seems to have been renewed in the same general area, and the Loup Fork formation, thin but extensive, was spread out over great areas, from South Dakota to Mexico. The lacustrine phases of this formation are probably less extensive than the subaerial.[14] To the north, the Loup Fork beds are often unconformable on the White River beds and like the latter have given rise to “bad land” topography. Lake and other terrestrial deposits, largely of volcanic material. are known north of the United States, especially in that pari of British Columbia[15] between the Coast and Gold ranges. Miocene deposits are known in Alaska, but erosion rather than deposition was the dominant process there so far as present data show.
Igneous activity during the Miocene. The wide-spread igneoul activity which began with the close of the Cretaceous continued, and perhaps reached its climax during the Miocene, Igneous materials abound in the sedimentary formations of the system [p. 813] throughout the west, and igneous activity affected nearly or quite every state west of the Rocky Mountains, and the eruptions were from fissures as well as volcanoes. Among the conspicuous centers of activity ’ the basin of the Columbia[16] and the Yellowstone National Park[17] may be mentioned. Locally, forests were buried by the volcanic ejecta, and in favorable situations their trunks were petrified (Fig. 548) . Great areas of the sedimentary beds of the period are concealed by the lavas, but the extrusions were by no means confined to the areas where sedimentation was in progress. The lavas of at least a considerable part of 200,000 or 300,000 square miles of lava-covered country in the western part of the United States issued during the Miocene period, or during the time of crust al deformation which brought it to a close.
Volcanoes were active in the Antillean region of Central America and the West Indies, and the Andean system of South America, as well as in North America.
Close of the Miocene. Slow warpings of the surface seem to have been in progress throughout the Cordilleran region during the Miocene period, accompanied by faulting and vulcanism, and [p. 814] locally, by pronounced orogenic movements.[18] But toward the close of the period movements were more general. Pronounced deformative movements affected the coastal regions of Oregon[19] and northern California, tilting and folding the Miocene and older formations. The principal folding of the existing Coast Ranges of both these states has been assigned to this time[20] but it now appears that some of the deformations heretofore referred to the end of the Miocene, took place after the Early Miocene (p. 808). The Cascade Mountains of Washington were in process of growth at this time.[21]
[p. 815]
Similar movements appear to have been wide-spread east of the coast, resulting, in some places, in the deformation of strata heretofore horizontal, but more commonly affecting formations and areas which had suffered deformation at some earlier time. In northern California, the deformation was such as to emphasize the central valley of the state though raising its northern part. Deformation and faulting seem also to have been wide-spread and pronounced in the Great Basin region, and elsewhere.
The later part of the period was perhaps the time when the greater relief features of the rugged west, as they now exist, were initiated. The great relief features of earlier times appear to have lost their greatness before the end of the Miocene (p. 810) . After the movements of the late Miocene had been accomplished, it is probable that the western part of the continent had a topography comparable, in its relief, to that of the present, though by no means in correspondence with it. The details, and even many of the larger features, of the present topography are of still later origin. Subsequent changes have been the result of (1) deformation, largely without notable folding, (2) faulting, (3) the extrusion of lava, and (4) extensive degradation and aggradation, by running water, by ice, and by wind.
In the eastern part of the continent, the geographic changes were less considerable, though the Atlantic and Gulf regions seem to have emerged, transferring the coast-line to some such position as it has to-day.
Foreign
Europe. The relations of sea and land remained much as in the early Tertiary, though the area of the sea was somewhat restricted [p. 816] in northern Europe, and extended in the southern part of the continent. Non-marine formations have much representation in this, as in most other post-Paleozoic systems. Some of the nonmarine formations are of brackish-water origin, and some of fresh. The marine beds occur chiefly along the Atlantic and Mediterranean coasts. The marine Miocene of Germany, Holland, and Belgium, is largely buried beneath glacial drift, and the exposed parts of the system are chiefly of non-marine origin. They include coal and tuff, besides the commoner clastic sediments. Thick conglomerates (3,900-5,900 feet) of early and Middle Miocene age are found along the north base of the Alps (Rigi), and tell something of the relief of the Alpine region at the time.
From the shallow epicontinental sea which covered part- ag Belgium and France, there may have been a sea connection by way of the Garonne, with the Mediterranean along the northern base of the Pyrenees. The strait of Gibraltar is thought to have been closed, and southern Spain joined to Africa; but there were perhaps straits across Spain, as across southern France, connecting the Atlantic with the southern sea.
Southern Europe appears to have been an extensive archipelago, the plateau of Spain, parts of the Pyrenees, the Alps, and the Carpathian Mountains, and portions of adjacent lands, being islands. The sea of southern Europe was expanded eastward far beyond the limits of the present Mediterranean. Late in the period, there was a notable withdrawal of the sea from the land.
The Miocene formations include all the ordinary sorts of sedimentary rocks common to marine and non-marine deposits, latter include not a little limestone of fresh-water origin, made partly from the secretions of algae. The system has great development in Italy, where it is said to attain a thickness of nearly 6,000 feet.
In spite of the wide sway of the southern sea of Europe, the Miocene formations do not appear at the surface in great a though found in all countries bordering the Mediterranean, both in Europe and Africa. In most of these countries, the lower formations are of marine origin, and the upper of brackish- or freshwater origin. They occur in Syria, but not in Arabia and Persia [p. 817] showing that the earlier connection between the Mediterranean and Indian Ocean regions had come to an end.
Close of the Miocene in Europe. In Europe, as in America, considerable disturbances occurred in the later part of the period, and at its close. Before its end, the Alps had had a period of growth, usually placed at the close of the Lower Miocene. The Apennines and other mountains of southern Europe also were in process of development during the later Miocene. In the Caucasus Mountains, Miocene beds occur up to heights of 2,000 meters. It will be seen, therefore, that deformative movements, involving the great mountain systems of the continent, were in progress in southern Europe during the later part of the Miocene period. As in America, widespread movements which were not notably deformative attended the growth of the mountains, with the result that the sea which had overspread southern Europe was greatly restricted, though not reduced to its present size. Igneous activity appears to have attended the movements of the time, but not on so great a scale as in North America.
Other continents. The Miocene of Asia has not been generally separated from the other Tertiary formations, but is known to be widely distributed in the southern part of the continent.[22] In Japan[23] and some other parts of northeastern Asia, the Tertiary (Miocene?) contains petroleum and metaliferous veins. A rich Miocene fauna, both marine and terrestrial, is found in Java.
In Africa, Miocene formations occur in Algeria and in Lower Egypt. Australia and New Zealand are rich in Miocene beds, some of which are marine, and some terrestrial. Igneous rocks are associated with the sedimentary. The beds are found up to heights of 4,000 feet, giving some clue to the extent of post-Miocene crustal deformation here.
In South America, Miocene beds probably occur in the western coast, and are known to have extensive development on the eastern plains of the southern part of the continent,[24] where the distinction between the Upper Oligocene and the Miocene is not sharp. The [p. 818] lower part of the Oligocene-Miocene series (Patagonian beds) is marine, while the upper part (Santa Cruz) is of fresh-water on The terrestrial faunas of this region are strikingly similar to the Miocene and later faunas of Australia and New Zealand. This relationship has caused speculation as to an Antarctic continent connecting these regions.
Arctic latitudes and climate. Miocene beds are somewhat widely distributed in the Arctic regions and seem to be largely of terrestrial origin, with the fossil floras indicating a warm temperate climate. Forty-six of the 137 species of plants found in North Greenland[25] (Lat. 70° and less) , including species of sequoia and magnolia, are also found in central Europe, and the floras of Spitzbergen and Grinnell Land were hardly less luxuriant.
Curiously enough the Miocene plants of Alaska, Kamschatka, and Japan indicate a climate cooler than that of the higher latitudes. It seems probable that this apparent discrepancy is the result of imperfect correlation, the fossils indicating these inharmonious conditions not being contemporaneous. The fauna of New / land is distinguished by the great size of some of its molluscan shells. Both the flora and fauna have a tropical aspect, the fruit of the palm having been found as far south as latitude 45°.
The Land Plants
The mid-latitude flora of the Miocene records the gradual disappearance of subtropical types, and an increase of deciduous trees. This is particularly true of North America, where the flora came to resemble that of to-day in somewhat lower latitudes, and is indeed its predecessor. An important feature in North America was an increase in the grasses, with its appropriate effect on mammals.
How far the gradual removal to the south of the forms now regarded as tropical or subtropical, and how far the concentration at the north of the forms that now characterize those lat it;, were the result of a natural segregation of the previously mingled forms, and how far the result of changes of climate, it is perh unsafe to say; it has usually been attributed to the latter.
[p. 819]
The Land Animals
The earlier fauna. The early Miocene (John Day epoch[26]) land fauna of North America was very distinct from the late Miocene (Loup Fork epoch). The earlier resembled the Oligocene (White River) fauna in general aspect, but most of the mammalian genera and nearly all the species were new and more modern. Primitive carnivores were succeeded by true carnivores, chiefly of the cat and dog families. Several branches of the perissodactyls had disappeared, reducing them essentially to their three persistent lines, exemplified by the horse, the tapir, and the lowland rhinoceros. The eventoed branch also had developed into modern lines. Rodents were abundant, including squirrels, beavers, gophers, rabbits, etc.
The later fauna. Elephants. A notable addition to the mammalian fauna of North America in the late Miocene, was the proboscidians. Primitive proboscidians lived in Egypt at least as early as the Middle Eocene, and in Europe in the early Miocene. Elephants reached North America in the late Miocene, and South America in the Pliocene.
[p. 820]
Ruminants. Much more important was the immigration of the modern ruminants. Certain branches of the ruminants had been represented previously, but the great ruminant group that later formed so important a part of the fauna does not seem to have descended from the early North American forms, but to have immigrated from Eurasia. They are first recorded in the Loup Fork be< Is. The first immigrants belonged to the deer and ox families. The earliest known deer (excluding Protoceras) were from Europe. They were hornless, as are their surviving relatives in Asia. By the middle of the Miocene, some of the males had acquired small twopronged deciduous antlers, fixed on long bone pedicles. About the close of the period, three or four prongs were added, and in the Pliocene the antlers were variously branched and the pedicles shortened to insignificance, as in most living deer. This historical evolution of the antlers is reproduced in the individual history of the modern male deer. Born hornless, he acquires in successive years the single, the bifurcate, and the more and more complexly branched antlers that mark the history of the race. It was in the bifurcating stage that the deer appeared in America, its antlers being simple and small, but variable. The skeletons imply lightness and speed, but not to the same degree as later.
There is some doubt as to the precise stage to which the remains of bison found in Nebraska and Kansas are to be assigned. They have usually been referred to the Lower Pliocene; but Matthew assigns them to the Upper Miocene, and Williston to the early Pleistocene.[27] The earliest known bisons on the Eurasian continent have been found in the Siwalik formation of India, which is regarded as Lower Pliocene.
The more primitive genera of camels had disappeared, but 15 species of more modern type have been identified from the Fork formation. The family seems to have been confined still to North America.
The evolution of the horse. The Miocene was a great epoch ii the evolution of the horse; Anchippus, Protohippus, Pliohippus (Merychippus), Hipparion, and other genera flourished and deployed into forty or more species. They were still three-toed, but [p. 821] the two lateral toes were dwarfed and did not usually touch the ground, while the central one was strengthened and bore all the weight. A large group of structural features were being modified concurrently with the feet, to fit the evolving horse to dry plains and grassy food (Fig. 551). The elimination of the side toes, the lengthening of the limbs, the change of the joints to the “pulleywheel” type, the concentration of the limb muscles near the body to reduce the weight of the parts most moved, and the consolidation of the leg bones, were modifications in the interest of speed and strength. An elongation of head and neck was necessary to reach the ground. The front teeth were reduced to chisel-like, cropping forms, somewhat resembling those of the rodents, while the molars evolved a tortuous distribution of the enamel so flanked by dentine and cement that the differences of wear gave rise to ridges of enamel suited to grinding, and protected against breaking by supporting dentine and cement on either side. The teeth were also gradually elongated to provide for the great wear caused by the dry silicious grasses.[28] It is probably as safe to infer a development of dry, grassy plains from this evolution of the horse, as to infer climatic and topographic conditions from plants and other organic adaptations.
[p. 822]
[p. 823]
Tapirs and rhinoceroses. Tapirs were but meagerly represented, but rhinoceroses, though the running and swimming branches had disappeared, were prominent. The American species were still mainly hornless (Aceratherium) , though slight indications of horns appeared in one genus (Diceratherium) . Two-horned species appeared during the period in Europe.
Carnivores. The carnivores were abundant, and had assumed forms referred with some doubt to the living genera Canis, Felis, Mustela, and Putorius. The dog family embraced numerous wolves and foxes; the cat family, panther-like animals and sabertoothed cats; the Mustelidae, weasel-like and otter-like forms, and an ancestral coon. The genera of the Loup Fork epoch were nearly all different from those of the John Day epoch, indicating rapid evolution. Other existing families of carnivores lived in Europe.
Other orders. Rodents were abundant, but neither insectivores nor primates are among the North American fossils. The development of the plains which favored horses, deer, and cattle, was obviously unfavorable to the lemuroids.
Primates. In the Old World, true apes had appeared. One type was a rather large annectant form, combining some of the characters of apes and monkeys; another was a generalized type related to the chimpanzee and gorilla, and about as large as the former. It is the view of some paleontologists that the ancestral branch of the Hominidae must have diverged from its relatives at least as early as this ; but on the origin of the Hominidae, the record throws no direct light.
The lower vertebrates. Little of moment is recorded relative to the lower vertebrates. Not much is known of American Miocene birds, but their advancement in later stages implies that they continued their evolution with measurable rapidity, a conclusion supported [p. 824] by the European evidence. Reptiles had very generally assumed modern forms, and were represented by turtles, snakes, and crocodiles. Amphibians came again to notice in the form of a large salamander, whose remains, found at Oeningen, Switzerland, formerly attained an unworthy celebrity from false identification as a human skeleton, and from the application of the pretentious name Homo diluvii testis.
Summary. A general view of the American Miocene land fauna shows that the great order of ungulates took precedence in evolution, and that both the odd- and even-toed branches participated actively. Closely following these in importance, and dependent on them for the conditions of their evolution, came the carnivores. Rodents occupied a middle position, and insectivores and lemuroids declined notably.
The European record bears a similar general interpretation, with the ungulates somewhat less pronouncedly in the lead, the carnivores somewhat better deployed, and the proboscidian conspicuous factor. The important evolution of the higher primates seems to have been confined to the Old World.
The Marine Life
Provincialism dominant. The pronounced provincialism that had been inaugurated in the Oligocene epoch continued throughout the remainder of the Cenozoic era. There was some amelioration during the Miocene, but it was not marked. No essential relief possible so long as the shallow seas remained mere bordering tracts, as in North America, or mere bays and straits, as in Europe. 1 the narrow border tracts that were geographically continuous show signs of having been cut into biological sections by interrupting barriers. Such barriers had perhaps been operative in certain earlier periods, but their influence there is not so well record The land area being large, large rivers reached the coast here and there, and poured great volumes of fresh and muddy waters a< the shore belt, doubtless forming barriers to some species, though probably not to all. The warpings of the crust probably projei peninsulas and submarine ridges out upon and perhaps across the continental shelf. These were not only harriers in themselves, but had an influence in directing the courses of the coast currents. Differences of climate in different latitudes had been developed apparently, and cold and warm currents were probably more pronounced than in earlier times, and their shiftings had still graver effects upon the faunas. So too, the lower temperatures in the northern shore tracts of the Atlantic and Pacific prevented their serving longer as migratory routes for warm-water species, and this tended further to intensify the provincial nature of the shallowwater faunas.
[p. 825]
[p. 826]
[p. 827]
According to Dall, the Chesapeake Miocene was ushered in by a marked faunal change due to a cold northern current driving out or destroying the previous warm-water fauna of the region, and bringing with it a cold-water fauna. There was a complete change of species, and even some genera were displaced. The fauna retained, however, a general molluscan aspect. Both the bivalves and the univalves gave proof of better adaptability to the vicissitudes of the coastal tracts than most other forms, and whether warm or cold waters prevailed, held their dominance. Figs. 552 and 553 show a few of the characteristic types. Compared with the Eocene group,Fig. 535, the resemblances will be found more striking than the differences.
Notwithstanding the provincializing agencies, there were many close correspondences between the faunas of the western and the eastern sides of the Atlantic,[29] probably due partly to intermigration and partly to parallel evolution.
The marine fauna of the Pacific coast indicates a climate but little warmer than that of the present, and this conclusion is reinforced by the plants of the Puget Sound region, which record | transition from the subtropical climate of the Eocene to the temjperate climate of the present. The fauna of the Upper Miocene lindicates a still closer approach to the present.[30]
For general summary of literature on the Miocene (Miocene and Pliocene) prior to 1892, see Dall and Harris, Bull. 84, U. S. Geol. Surv. The bibliography up to 1896 is found in the 18th Ann. Rept., U. S. Geol. Surv., Pt. II (Dall). ↩︎
Reports of the State Geologist of New Jersey, especially Report of 1892. ↩︎
Clark, Maryland Geol. Surv., Vol. I, and volume on the Miocene, 1904. ↩︎
Penrose, Bull. 46, U. S. Geol. Surv. ↩︎
Hayes, Bull. 213, U. S. Geol. Surv., p. 346. ↩︎
Arnold, Ralph, Jour. Geol., Vol. XVII. ↩︎
Eldridge, Bull. 313, U. S. Geol. Surv.; Arnold and Anderson, Bull U. S. Geol. Surv. ↩︎
Diller, Coos Bay and Port Orford folios, U. S. Geol. Surv. ↩︎
Turner, The Geology of Mount Diablo, Bull. Geol. Soc. Am., Vol. ↩︎
Lawson and Palache, Bull. Dept. Geol., Univ. of Cal., Vols. I and II; Ashley, Jour. Geol., Vol. Ill, p. 434; and Fairbanks, Jour. Geol., Vol. VI, p. 561. ↩︎
Whitney, The Auriferous Gravels of the Sierra Nevada of Calif. ; Turner, 14th Ann. Rept., U. S. Geol. Surv., 1894; Lindgren, Jour. Geol., Vol. IV, 1896, pp. 881-906; Diller, Jour. Geol., Vol. II, pp. 32-54. See also folios of the Gold Belt of Calif., U. S. Geol. Surv. ↩︎
Diller, Jour. Geol., Vol. II, pp. 33-54. ↩︎
Whitney, op. cit. ↩︎
Haworth, Univ. Geol. Surv. of Kan., Vol. II, p. 281. ↩︎
Dawson, G. M., Trans. Royal Soc. of Canada, 1890. ↩︎
Landes, Wash. Geol. Surv., Vol. II, and Smith, G. O., Ellensburg folio, U. S. Geol. Surv. ↩︎
Western folios, U. S. Geol. Surv., notably the Yellowstone National Park folio. Most of the folios showing Neocene formations show volcanic rocks of Neocene age. ↩︎
Ashley, Jour. Geol., Vol. Ill, p. 434; Whitney, Geol. of California, I ↩︎
Diller, 17th Ann. Ilept., U. S. Geol. Surv. ↩︎
Ashley, op. cit. ↩︎
Willis, Professional Paper 19, U. S. Geol. Surv. ↩︎
Oldham, Geol. of India. ↩︎
Geology of Japan, Imp. Geol. Surv., 1902. ↩︎
Hatcher, Sedimentary Rocks of Southern Patagonia, Am. Jour, of Science, Vol. IX, 1900; and Ortmann, Princeton Univ. Repts. of Expedition to Patagonia, Vol. IV, Pt. II. ↩︎
Heer, Flora Fossilis Arctica, 1868-83, and Q. J. G. 8., 1878. Th< some question as to the Miocene age of these fossils. ↩︎
Perhaps all the John Day beds should be classed as Oligocene (p. 781). ↩︎
Bull. Am. Mus. Nat. Hist., XII, 1899, p. 74. ↩︎
An excellent recent statement of the evolution of the horse, admirably illustrated, is given by Matthew, Sup. to Am. Mus. Jour., Vol. Ill, No. 1, Jan., 1903. ↩︎
Md. Geol. Surv., Miocene volume, 1904, pp. 151-153. I ↩︎
Arnold, Ralph, Jour. Geol., Vol. XVII. For Miocene marine fossils of the Pacific coast, see Dall, Professional paper 59, U. S. Geol. Surv. ↩︎