Page:Popular Science Monthly Volume 3.djvu/301

Rh This theory, so novel, so startling, met with various acceptance. By some it was loudly scouted as the product of the imagination solely; and was classed by Prof. B. Studer, a savant of the Continent of Europe, with the poetical Indian legends, wherein the periods of heat and life are made to alternate with periods of freezing and death. But its force lay in the inherent evidence of candor, and honesty in the statement of facts about which there could be no dispute. By the most enlightened geologists, both of the Old World and the New, it was received as a flood of light cast on what had before been dark and unexplained; and it was accepted with some caution and exceptions by such men as Prof. Buckland, Sir Charles Lyell, and Prof. Edward Hitchcock. At the present day but few geologists can be found in this country who do not admit the reality of the glacial epoch.

But, while it is true that but few geologists can be found in this country who do not admit the truth of the glacier theory of Prof. Agassiz, it is also true that a great many, perhaps the majority, also adhere to the iceberg theory of Peter Dobson. The two theories at first came in violent conflict. They diverged at the outset. One required the continent below the ocean, and the transportation of bowlders and other drift by floating ice; the other required it elevated high above the ocean, and the transportation of the drift by ice in the form of continental glaciers. How, then, can the same person hold to both theories?

Soon after the promulgation of the glacier theory by Prof. Louis Agassiz, Mr. Charles McLaren attempted to make it harmonize with the iceberg theory. He was seconded in the effort by Prof. Edward Hitchcock, who invented the term aqueo-glacial, to express the force, or forces, that operated to disperse the materials of the drift. In explaining the meaning of that term, he says, however, he cannot admit the glacier theory of Prof. Agassiz, and apply it unqualifiedly to this country; but, while acknowledging himself greatly indebted to Agassiz, he thinks that icebergs were the principal agents in transporting the drift. In the years 1841 and 1842 Sir Charles Lyell visited this country. His observations on the drift, published in various scientific journals, and repeated in his book of "Travels in North America," in 1845, furnish the basis for the most plausible union of these two theories. He divides the drift epoch into four parts:

 1. The period of emergence of the land, during which some of the bold, rocky escarpments of the continent were formed. 2. A gradual subsidence and moderate submergence of the interior portions of the continent, during which icebergs floated over the surface of the ocean, grinding and marking the rocks. 3. The deposition of the clay, gravel, and sand, of the drift, with occasional fragments of rock, the last through floating ice. 4. Period of reëlevation and formation of lake-terraces.

Although not professedly aiming to reconcile the iceberg theory