5 Chemung     . . . . . . sandstones and sandy shales
4 Hamilton    . . . . . . shales and sandstones
3 Corniferous . . . . . . limestones
2 Oriskany    . . . . . . sandstones
1 Helderberg  . . . . . . limestones

The Helderberg is a transition epoch referred by some geologists to the Silurian.  The thin sandstones of the Oriskany mark an epoch when waves worked over the deposits of former coastal plains.  The limestones of the Corniferous testify to a warm and clear wide sea which extended from the Hudson to beyond the Mississippi.  Corals throve luxuriantly, and their remains, with those of mollusks and other lime-secreting animals, built up great beds of limestone.  The bordering continents, as during the later Silurian, must now have been monotonous lowlands which sent down little of even the finest waste to the sea.

In the Hamilton the clear seas of the previous epoch became clouded with mud.  The immense deposits of coarse sandstones and sandy shales of the Chemung, which are found off what was at the time the west coast of Appalachia, prove an uplift of that ancient continent.

The Chemung series extends from the Catskill Mountains to northeastern Ohio and south to northeastern Tennessee, covering an area of not less than a hundred thousand square miles.  In eastern New York it attains three thousand feet in thickness; in Pennsylvania it reaches the enormous thickness of two miles; but it rapidly thins to the west.  Everywhere the Chemung is made of thin beds of rapidly alternating coarse and fine sands and clays, with an occasional pebble layer, and hence is a shallow-water deposit.  The fine material has not been thoroughly winnowed from the coarse by the long action of strong waves and tides.  The sands and clays have undergone little more sorting than is done by rivers.  We must regard the Chemung sandstones as deposits made at the mouths of swift, turbid rivers in such great amount that they could be little sorted and distributed by waves.

Over considerable areas the Chemung sandstones bear little or no trace of the action of the sea.  The Catskill Mountains, for example, have as their summit layers some three thousand feet of coarse red sandstones of this series, whose structure is that of river deposits, and whose few fossils are chiefly of fresh-water types.  The Chemung is therefore composed of delta deposits, more or less worked over by the sea.  The bulk of the Chemung equals that of the Sierra Nevada Mountains.  To furnish this immense volume of sediment a great mountain range, or highland, must have been upheaved where the Appalachian lowland long had been.  To what height the Devonian mountains of Appalachia attained cannot be told from the volume of the sediments wasted from them, for they may have risen but little faster than they were worn down by denudation.  We may infer from the character of the waste which they furnished to the Chemung shores that they did not reach an Alpine height.  The