|NORTH AMERICA IN THE ICE PERIOD.|
PROFESSOR OF GEOLOGY AND PALEONTOLOGY IN COLUMBIA COLLEGE.
ALTHOUGH the glaciated area on our continent has been as yet but partially explored, abundant proof has been gained, as it seems to me, of the truth of the following propositions, viz.:
1. That glaciers once covered most of the elevated portions of the mountain-belts in the West as far south as the thirty-sixth parallel, and all the eastern half of the continent to the fortieth parallel of latitude.
2. That the ancient glaciers which occupied the area described were not produced by local causes, but were the exponents of a general climatic condition.
3. That they could not have been the effect of a warm climate and an abundant precipitation of moisture, but were the results of a general depression of temperature, and therefore afford proof of the truth of what is called the glacial theory.
The facts and arguments which sustain these propositions may be briefly summarized as follows:
The glaciation of the Sierra Nevada is general and very striking. It has been studied by Whitney, King, Brewer, Le Conte, and others, including the writer, who have given abundant proof that all the highest portions of the range were once covered with snow-fields, and that glaciers flowed from these down the valleys on either side. Mount Shasta once bore many great glaciers, of which miniature representatives still remain; the Cascade Mountains exhibit, perhaps, the most impressive record of ice-action known; all the higher portions of the range are planed and furrowed by glaciers which descended into the valley of the Des Chutes on the east, and the Willamette on the west, as shown by my observations in 1855, at least twenty-five hun-