Geology Volume 3 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1907 Excerpt: ... associated with analogous deposits on the Great plains, and through them with the intermontane deposits of the west, already mentioned. The term Lafayette has been usually applied only to the formation on the slope between the Appalachians and the Atlantic, to that in the Mississippi basin below the junction of the Ohio, anil to the Texan tract. The formation thus limited has been estimated to have an area of from 200,000 to 250,000 square miles. It lies like a blanket over the eroded edges of all the older formations of the region, from the pre-Cambrian to the Miocene. It extends inland from the coast up to varying altitudes. In Mississippi, its landward edge is said to reach an elevation of 500 or 600 feet; in Tennessee, 800 feet; at Austin, Texas, 500 feet, and near the Rio Grande, 1000 feet1; but on the Atlantic slope, the elevation is generally less. At its mountaihward edge, ragged belts of the Lafayette formation follow the valleys up into the mountains, and unless our identifications be in error, they reach back through the gaps, where they are locally interrupted, into the intermontane valleys. Between the valley phases, its mountainward edge recedes and is ragged, and has not yet been carefully mapped. At its seaward margin, the formation is more or less completely concealed by younger beds. It is not to be doubted that the Lafayette formation or its equivalent passes out to sea beneath these younger beds. Indeed, there is some reason to believe that at some point s it is replaced within the present land-area, by marine beds, as such a formation is very liable to be where the plain on which it was deposited slopes gently to the sea. But such marine deposits as can be correlated, even hypothetically, with the Geology of Tenn. (Bluff Gravels), and ...