Henderson, J. “Extinct glaciers of Colorado.” Colo. Univ. Studies, 3, 1905, p. 39.
Gilbert, G. K. “Lake Bonneville.” Washington, U.S. Geol. Survey Monograph I, 1890.
Russell, I. C. “The geological history of Lake Lahontan.” Washington, U.S. Geol. Survey Monograph XI, 1885.
Coleman, A. P. “An estimate of post-Glacial and interglacial time in North America.” Rep. 12 Internat. Congr. Geol., 1913, p. 435.
CHAPTER IX
CENTRAL AND SOUTH AMERICA
The scarcity of data which was bewailed in dealing with Asia is still more marked in the case of South America, and it will be necessary to present the glacial history of that continent in the barest outline only. This is the more unfortunate as the chain of the Andes, extending from north of the equator to high southern latitudes, is of enormous importance in glacial theory, and especially in the question of simultaneity of glaciation in the two hemispheres.
The beginnings of glaciation in South America are obscure. The distribution of animals shows that towards the close of the Tertiary the Falkland Islands were greatly elevated and were united to Tierra del Fuego and Patagonia, and this enlarged land area was connected in some way with Australia and Tasmania, but the mode of this latter connexion is not definitely known. This question will be discussed more fully in [Chapter XI]; it is sufficient to say here that the amount of elevation may have reached 12,000 feet in Tierra del Fuego. Equatorwards the elevation diminished, and near the equator the land probably lay somewhat lower than now.
In South Georgia the present glaciers greatly expanded, until practically the whole island was buried in ice, and the same is true of the Falkland Islands and Tierra del Fuego, only the highest peaks remaining above the ice. In the latter district there is some evidence of two glaciations separated by an interglacial, the earlier glaciation being due to a regional ice-sheet and the later to smaller valley glaciers. The intricate coast-line of the Falkland Islands and Tierra del Fuego points to fiord erosion by ice which extended well beyond the present limits of the land, and can only have occurred during considerable elevation. As to the character of the interglacial, little is known. In the Falklands there is a bed of black vegetable soil full of tree-trunks, indicating the existence of luxuriant forests and a temperate climate. This deposit is overlain by boulder-clay, and may be either interglacial or pre-glacial, but since it was formed when the land stood at a comparatively low level, while we have reason to believe (see [Chapter XII]) that during the close of the Tertiary period these islands were greatly elevated, it is probably an interglacial formation, and indicates a great amelioration of climate. In Gable Island, Tierra del Fuego, Halle found beneath boulder-clay a Quaternary fauna of barnacles and marine mollusca indicating a climate slightly warmer than the present, and this probably belongs to the same period. To the concluding stages of the Glacial period in the Falklands belong the curious “stone rivers,” great streams of moss-grown boulders which fill the valleys, and under the influence of temperature changes are probably still slowly advancing.
Passing further north to the Andes, between 39° and 44° south latitude, the glaciation was not so severe, and its records are therefore clearer. The first result of elevation was the cutting of deep canyons by the rivers. This was followed, possibly without much further elevation, by a fall of temperature, which in this connexion may be attributed to the extension of the Antarctic and Tierra del Fuego ice-sheets. Glaciers now developed and spread down the canyons, leaving moraines of great volume and height, associated with all the other criteria of glaciation. The snow-fields from which these glaciers originated lay between 5000 and 6000 feet above the sea, and the snow-line lay at about 3000 feet instead of above 6000 as at present.