Page:Popular Science Monthly Volume 30.djvu/20

10 the interval represented by peat-beds between the first and second bowlder clays, was that of a cool climate, and the interglacial beds have not been traced beyond Scarboro Heights, on Lake Ontario.

Facts similar to those from which we have sketched the history of the Ice period in North America, observed in Europe and Asia, afford abundant evidence that the conditions which existed here prevailed over all the northern hemisphere. In South America also similar phenomena have been observed and reported by many geologists. Hence, any explanation offered of the records of the glacial period found here must be comprehensive enough to include the whole great field; and the difficulties which here oppose the acceptance of a theory that is only local in its scope, grow until they become insurmountable. That the conditions which prevailed simultaneously in different parts of the northern hemisphere during the Ice age were synchronous with similar conditions in the southern hemisphere is not proved, nor is it probable that it is susceptible of proof. By many, perhaps most geologists these conditions are supposed to have alternated at the north and south. This much, however, we are justified in asserting, that at an epoch holding the same relative position in geological history north and south of the equator, either simultaneously or alternately, cold climatic conditions prevailed in both hemispheres and left records that are alike in character and import.

An inquiry into the nature of the cosmical influence which we must credit with the phenomena of the Ice period would lead beyond the scope of this paper, and open questions too broad and suggestive to be settled or even adequately discussed in the space at our command. I shall, however, have accomplished the end I had proposed to myself if I have shown—1. That the Ice period was a cold period. 2. That the record of the Ice period on our continent is more complete and impressive than it has been represented to be. 3. That it is the product of general and not of local causes. 4. That these causes were not topographical or even telluric, but extraneous and cosmical.

The question here passes rather into the hands of the astronomer and physicist. The work of the geologist is done when he has shown that the complete solution of the problem does not lie within his domain; that no telluric agency is adequate to produce the phenomena; and that some cosmical cause, such as a variation in the heat radiated by the sun, as suggested by Newcomb, changes in the eccentricity of the earth's orbit, as advocated by Croll, or some other general and all-powerful influence, must be credited with effects as wide-spread and stupendous as those the Ice period has left behind it.