The Ancient Lakes of Western America, their Deposits and Drainage*
1870; Nature Portfolio; Volume: 2; Issue: 45 Linguagem: Inglês
10.1038/002385a0
ISSN1476-4687
Tópico(s)Water Quality and Resources Studies
ResumoTHE wonderful collections of fossil plants and animals, brought by Dr. Hayden from the country bordering the Upper Missouri, are from deposits made in extensive fresh-water lakes which at one time occupied much of the region lying immediately east of the Rocky Mountains. The water of these lakes was first salt or brackish, as the remains of oysters and similar estuary forms show. By continental elevation the whole country west of the Mississippi was raised out of the cretaceous sea, and these estnaries became lakes inclosed by raised dry land. The knowledge of this country from the Mississippi to the Pacific Ocean has been accumulated by various explorers besides the writer, as Dr. Hayden, Mr. George Gibbs, Professors W. P. Blake and Thomas Antisell, and Prof. J. D. Whitney and the State Geological Survey of California, and Baron Richtofen, the lamented Rémond, Drs. Shiel, Wislizenus, and others. Besides Mr. Clarence King has explored a large tract of this country, but his very important contributions have not, as yet, been made public. The general character of the topography of the region west of the Mississippi has been given by these great lines of elevation traversing the country from north to south. There are the Rocky Mountains, the Sierra Nevada, and the Coast Ranges. The last is the most modern, and is composed, for the most part, of Miocene Tertiary rocks. Parallel with this lies a narrow trough, in California traversed by the Sacramento and San Joachin Rivers, encroached on by the mountains at places, but still in Oregon and Washington, traversed by the Willamette and Cowletz Rivers. These two sections are drained through the Golden Gate and Columbia. The mountain barriers formerly caused the valleys to consist of great inland lakes, which are now only represented by the chain of small pieces of water still to be seen in that region of country. East of the Sierra Nevada and between it and the Rocky Mountains is another still larger basin. For a thousand miles it has no openings to the westward, which are less than five thousand feet above the sea, but at three points there are gateways, which may be passed, but little above the sea level. These are the canons of the Sacramento (Pit River), the Klamath, and the Columbia. These have been out through by the drainage of the interior of the continent. The former beds of the lakes have thus been left dry and waste—the only real desert on the North American continent. The Sierra Nevada is older than the Coast Ranges, and projected above the ocean, though not to its present altitude, previous to the Tertiary and even Cretaceous ages. This we learn from the fact that strata belonging to these formations cover its base. The mass of the Sierra Nevada is granitic rocks and metamorphic slates, proved Dy the California Survey to be triassic and jurassic. These slates are traversed by the gold-bearing quartz. East of the Sierra Nevada is a high and broad plateau five hundred miles wide, and from four to eight hundred feet in altitude, and reaches south into Mexico. This mountain belt was once the margin of the Pacific Ocean. Its crest is crowned by volcanic cones like gigantic towers of a fortification. The central portion of this plateau was called by Fremont “the great basin,“ as it forms a hydrographic basin drained by the Columbia and Colorado. The former makes its way to the ocean through a gorge in the Cascade Mountains, whilst the latter escapes to the south through a series of canons, of which the most important is nearly a thousand miles in length, and from three to six thousand feet deep. In vol. vi. ol the Pacific Railroad Reports the country of the Columbia is described and the reasons for concluding that it had cut its way through the Cascade Mountains, and similar facts were observed in the district drained by the Klamath and Pit Rivers. Certain peculiarities are to be seen in the country between the Sierra Nevada and Rocky Mountains. In the northern and middle portions of the great table lands the surface is somewhat thickly set by short and isolated mountain ranges, sometimes called “the lost mountains.” These rise like islands above the level of the plain, and are generally composed of volcanic or metamorphic rocks. The spaces between them are level desert surfaces. Towards the north and west, on the tributaries of the Columbia, Klamath, or Pit Rivers, the plateau is cut by these streams, and the deposit can be examined. The rocks are nearly horizontal, some are coarse volcanic ash, with fragments of pumice and scoriæ. Others denominated “concrete”resemble the old Roman cement. Many are quite white, and are generally known as “chalk-beds,” though they contain no lime. The late Prof. J. W. Bailey determined these to consist of the remains of fresh-water species of Diatomaceæ. The stratification and horizontality of these beds show them to have been thrown down from great bodies of water which once covered the greater part of these level plains. From south-western Idaho and eastern Oregon have lately been brought large collections of animal and vegetable fossils, of great variety and interest. The plants were mostly collected by the Rev. Thomas Congdon, of the Dalles, Oregon, at great risk of life and while exposed to great hardships, on the flanks of the Blue Mountains. They are apparently Miocene, forming twenty or thirty species, nearly all new, and which represent a forest growth as varied and luxurious as can be found on any portion of the continent. The animal remains came mostly from the banks of Castle Creek in the Owyhee district, Idaho. These were sent by Mr. J. W. Adams of Ruby City. They consist of bones of the mastodon, rhinoceros, horse, elk, and other large mammals of which the species are probably in some cases new, in others identical with those obtained from the deposits examined by Dr. Hayden. There are also bones of birds and great numbers of the bones and teeth of fish. These last are cyprinoids applied to Mylopharodon, Milocheilus, & c., some three feet and more in length. Also many fresh-water shells, as Unio, Corbicula, Melania, and Planorbis. These illustrate the inhabitants of the extinct lakes, which were of a much larger size and greater depth than the great fresh-water lakes which now lie upon our northern frontier. Between these were areas covered with a luxuriant and beautiful vegetation and inhabited by herds of elephants and other great mammals. In the streams were numbers of fish and mollusks of species now extinct. Gradually these lakes evaporated and at last became dry. In the Klamath lakes and Suisun Bay we have their remanents, whilst on the Columbia the drainage streams have cut canons two thousand feet deep. At times the peace and quiet of this country were disturbed by violent volcanic eruptions from the peaks of the Sierra Nevada, which ejected showers of ashes covering the land and filling the lakes, as is seen in the strata now existing, some ten and twenty feet thick. Sometimes lava was thrown out and covered hundreds of miles of surface, and is now seen as solid basalt. Then quiet reigned, and new fresh-water deposits were formed, only to be succeeded by other volcanic disturbances. Some parts of this plateau have not been drained, and the remains of the ancient lakes now exist as Salt Lake, Pyramid Lake, and others. These are gradually diminishing, as is to be seen by indications all around their borders, where we can trace ancient shore lines. The alkali plains and salt flats mark the places of dried-up lakes; all of these still existing being excessively salt. This is the state of things at the north. In the south, the great Colorado plateau is without mountain barriers or local basins, and thers are few traces of extinct lakes. This arid district was once a beautiful and fertile plain, drained by the Colorado, which, on the western margin poured over a precipice five thousand feet or more high, into the Gulf of California, which then reached several thousand miles farther north than it does now. In time the river cut its way farther back through the subjacent rocks, and at last formed that remarkable gorge, nearly a thousand miles long and three to six thousand feet deep. As the channel deepened, the country around became dryer, until it was the arid plain we find it now. Almost no rain falls on this plain, there-fore the walls of the canon remain sharp-cut precipices unaffected by moisture. On the east of the Rocky Mountains is the great plateau country of the plains, which differs from the country to the west, by not being bordered on its east by a mountain chain, but sloping gradually to the Mississippi. Its surface was also covered by great fresh water lakes, larger, if not more numerous, than those now existing on our northern boundary. From the northern portion of this plateau Dr. Hayden has brought his specimens, and he has there obtained a harvest of scientific truth which will form for him an enduring and enviable monument. He has studied the deposits which accumulated in these lakes, and they are very rich in specimens of both animal and vegetable life. The vertebrate remains have been studied by Dr. Leidy, who has published his investigations in the splendid monograph so well known, and which forms a contribution to palæontology, not second in value or interest to that made by Cuvier, by his illustrations of the fossils from the Paris basin, nor to that of Falconer and Courtly, descriptive of the Sewalik hills of India. The first instalment of the plants have been described by Dr. Newberry, in the report of Colonel W. F. Reynolds, U.S.A., not yet published. The descriptions are published in the Annals of the Lyceum of Natural History of New York, vol. 9, 1868. The general conclusions from these examinations have greatly enlarged the flora of the Tertiary and Cretaceous periods. Since then largely additional material has been collected by Dr. Hayden, Mr. Congdon and Dr. Le Comte, and Dr. New-berry; and in Alaska by Mr. W. H. Dall and Captain Howard, and by others in Greenland. The flora and fauna of the lake deposits on both sides of the Rocky Mountains apparently belong to one and the same geological age,
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