Page:Popular Science Monthly Volume 9.djvu/311

Rh terrestrial or cosmical, would produce all the phenomena of the Ice period.

Before we can certainly determine, however, what the nature of the cause producing the cold of the Ice period was, we must know more accurately where and how the cause operated. To accomplish this, observations must be made over all those portions of the northern and southern hemispheres where the traces of former glaciers are visible.

In a general way we know that there was a cold period throughout the northern hemisphere, as glacial phenomena are reported from Siberia and Northwestern America, somewhat similar to those which we find on the Atlantic coast. In regard to Siberia very much remains to be learned. Nearly the whole of the northern portion of this great area is flat, and is deeply covered with Quaternary deposits; and it has been conjectured that in the Ice period the shallow sea off the Siberian coast was solidly frozen throughout a great portion of its breadth, and thus formed an ice-dam, behind which the drainage of the northern slope accumulated alternately as sheets of ice and bodies of fresh water.

The northern portion of the interior of our own continent is said to be without 'distinct marks of glacial action. Should this statement be confirmed by further observation, it would not, however, be a formidable argument against a general Glacial period; for intense cold would leave no permanent record there, unless there was sufficient precipitation of moisture to form glaciers. As this region is now very dry and sterile, it was perhaps so through the Ice period, and snow at no time fell there in sufficient quantity to form glaciers. On the mountains of British America and Alaska, of Oregon and California, there are abundant evidences of glaciers far more numerous and extensive than any now existing; and these furnish demonstrative evidence that this region shared in the effects of a distinct Ice period. The slopes of the Cascade Mountains in Oregon are everywhere glaciated, and perhaps no more impressive record of the Ice period exists than that formed by the planed and furrowed surfaces, the roches moutonnées, etc., by which all the higher portions of the belt, twenty to thirty miles in width, are marked. No ice-sheet moved in that region from the north, as there was no district of northern highlands where continental glaciers could be generated; but the glaciers radiated east and west from various centres along the crests of the chain, and descended at least 2,500 feet below the present snow line. This I determined by actual barometric observation in many places, and I nowhere found the lower limit of glacial action, as the planed and furrowed surfaces passed beneath the alluvium of the lower valleys.

Whether there was a depression of the Western coast during the Champlain epoch, corresponding to that recorded along the shores of the Atlantic, we are as yet unable to say, as careful observations on