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290 with the glacier theory of M. Agassiz, Mr. Lyell's eminent authority would not permit the total extinguishment of the iceberg theory, and his generalizations have, perhaps, had more influence in directing the efforts of others in such reconciliation than the writings of any other man. It required but very slight changes in Mr. Lyell's method of dividing the history of the drift to evolve, in its present aspect, the latest theory of geologists touching the origin of the drift-deposits. Mr. Murchison, of England, coincides with Mr. Lyell in the submergence, or iceberg theory. Mr. J. D. Dana advocates the glacier theory in its fullest extent; but, although adopting also the term Champlain, he is far from admitting the recent enlargement of that epoch, so as to bring the continent beneath the water of the ocean as required by the supporters of the combination theory.

Professors E. W. Hilgard, of Mississippi, and J. S. Newberry, of Ohio, are among the most prominent advocates in this country of this new theory, resulting from the combination of the glacier and the iceberg theories. Dr. A. Winchell, of New York, also advocates the same.

It is as follows:

First. The glacier epoch proper.

During this epoch the continent was considerably elevated above its present level, especially in the north. This either produced, or was accompanied by, a greater degree of cold, the effect of which was to bring over the continent the vast sheets of ice in the form of continental glaciers, required by the hypothesis of Prof. Agassiz. During this epoch the rocks were scored, and many deep valleys were excavated. Large bowlders were transported to regions farther south.

Second. The submergence of the continent, attended by an amelioration of the climate and the disappearance of the glaciers, or their retreat to the far north. The assortment and stratification of the drift, produced by the glaciers, and the deposition of the great mass known as Erie clay, and other clayey portions of the drift-sheet. This condition of the continent was attended by the appearance of numerous icebergs which floated over the submerged land, and aided to transport the coarse drift, according to the hypothesis of Peter Dobson.

Third. The emergence of the continent with a halting progress, producing terraces and ridges marking the ancient levels of the ocean.

These three steps have been named by Prof. Dana, in their order, the Glacial Epoch, the Champlain Epoch, and the Terrace Epoch.

The studies of Professors Agassiz and Tyndall on the glaciers of the Alps, and of Dr. Kane on those of Greenland, have so fully demonstrated the adequacy of glaciers to produce all the effects attributed to them by the theory of Agassiz, that it is now very generally admitted that, wherever those phenomena are seen, glaciers must have existed.

Geology, having demonstrated thus the necessity for a period of cold, to account for the phenomena of the surface of the earth, labored