280 ANNUAL OF SCIENTIFIC DISCOVERY. 



have coincided in time with the submergence of the Sahara, namely, 

 the diversion of the Gulf Stream from its present course. Tne shape of 

 Europe and North America, or the boundaries of sea and land, departed 

 so widely in the glacial period from those now established, that we cannot 

 suppose the Gulf Stream to have tdken at that period its present north- 

 we.-.tern course across the Atlantic. If it took some other direction, the cli- 

 mate of the north of Scotland would according to the calculations of Mr. 

 Hopkins, suffer a diminution in its average annual temperature of 12 F., 

 while that of the Alps would lose 2 F. A combination of all the con- 

 ditions above enumerated would certainly be attended with so great a 

 revolution in climate as might go far to account for the excessive cold 

 which was developed at so modern a period in the earth's history. But 

 even when we assume all three of them to have been simultaneously in 

 action we have by no means exhausted all the resources which a difference 

 in the geographical condition of the globe might supply. Thus, for ex- 

 ample, to name only one of them, we might suppose that the hight and 

 quantity of land near the north pole was greater at the era in question 

 than it is now. 



The vast mechanical force that ice exerted in the glacial period has 

 been thought by some to demonstrate a want of uniformity in the amount 

 of energy which the same natural cause may put forth at two successive 

 epochs. But we must he careful, when thus reasoning, to bear in mind 

 that the power of ice is here substituted for that of running water. The 

 one becomes a mighty agent in transporting huge erratics, and in scoring, 

 abrading, and polishing rocks; but meanwhile the other is in abeyance. 

 When, for example, the ancient Rhone glacier conveyed its moraines from 

 the upper to the lower end of the Lake Geneva, there was no great river, 

 as there now is, forming a delta many miles in extent ; and several hundred 

 feet in depth, at the upper end of the lake. 



Antiquity of the Glacial Epoch. The more we study and compre- 

 hend the geographical changes of the glacial period, and the migra- 

 tions of animals and plants to which it gave rise, the higher our con- 

 ceptions are raised of the duration of that subdivision of time, which, 

 though vast when measured by the succession of events comprised in 

 it, was brief if estimated by the ordinary rules of geological classifi- 

 cation. The glacial period was, in fact, a mere episode in one of the 

 great epochs of the earth's history; for the inhabitants of the lands 

 and seas, before and after the grand development of snow and ice, 

 were ncarlv the same. As yet we have no satisfactory proof that man 

 existed in Europe or elsewhere (luring the period of extreme cold; 

 but our investigations on this head arc still in their infancy. In an 

 rarlv portion of the post-glacial period it has been ascertained that 

 man flourished in Europe; and in tracing the signs of existence, from 

 the historical a^es to those immediately antecedent, and so backward 

 into more ancient times, we gradually approach a dissimilar geo- 

 graphical state of things, when the climate was colder, and Avhen the 

 configuration of the surface departed considerably from that which 

 now prevails. 



Archaeologists are satisfied that in central Europe the age of bronze 

 weapons preceded the Roman invasion of Switzerland; and prior to 

 the Swiss-lake dwellings of the bronze age were those in which stone 

 weapons alone were used. The Danish kitchen-middens seem to have 



