CAUSES OF THE COLD OF THE ICE PERIOD. 289 



terrestrial or cosnrical, 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 Si- 

 beria and Northwestern America, somewhat similar to those which 

 we find on the Atlantic coast. In regard to Siberia very much re- 

 mains to be learned. Nearly the whole of the northern portion of 

 this great area is flat, and is deeply covered with Quaternary depos- 

 its ; 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 drain- 

 age 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, bowever, be a formida- 

 ble argument against a general Glacial period; for intense cold would 

 leave no permanent record there, unless there was sufficient precipita- 

 tion 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 roch.es moutonn&es, 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 gla- 

 ciers 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 



VOL. IX. 19 



