THE ICE PERIOD. 171 



level of seven thousand feet, and still others at a level of five 

 thousand feet above the bottom of the valley. 



Now, by the polished surface of the bottom of the valley, and 

 the polished and grooved surface of the sides of the valley, and 

 by the lateral moraines formed upon the terraces on the sides of 

 the valley, and the transverse moraines observed at the bottom 

 of the valley, across the valley, we can determine the successive 

 stages of any one of the glaciers of the valleys of the Alps. And 

 that survey has been made. It was begun in 1825 by De Cliar- 

 pentier. I took up the subject in 1827, and, with Prof. Guyot, 

 surveyed nearly the whole surface of Switzerland, with a view 

 to ascertain what had been the extent of the glaciers at the 

 earliest time of which we could obtain information by this 

 method ; and we ascertained that they had not stopped at the 

 lower part of the Alpine valleys ; that they had not stopped at 

 Meyringen, but had followed the inequalities of the Alpine slope 

 down to the plain of Switzerland. Nor did they stop there. 

 They crossed the plain of Switzerland and reached the plain 

 of the Jura, twenty-five miles to the north of the Alps. So 

 there was a time when the masses of ice which occupied Switzer- 

 land filled the wliole basin of Switzerland, from the Alps to the 

 Jura, and ascended the Jura to the height of three thousand 

 feet. Here, then, is as positive evidence as we can wish that 

 at one time the whole extent of that country was under ice. 



"With that information, I went further. I visited in 1840 the 

 British Isles, and discovered traces of the glacier in Scotland, 

 in England and in Ireland, and satisfied myself that that coun- 

 try at one time had been entirely under ice. Similar observa- 

 tions were made by other investigators, and, in consequence of 

 all these observations, the conviction gradually prevailed among 

 geologists that Europe had at one time a much colder climate 

 than now, and that the boulders of Scandinavian origin which 

 were found in northern Germany had been transported from Nor- 

 way and Sweden, across the Baltic, by masses of ice extending 

 from the North Pole across these regions to the more temperate 

 portions of Europe ; and gradually the evidence has been ob- 

 tained that an ice period once prevailed upon the surface of the 

 globe, during which the continent of Europe was all under ice. 

 The evidences by which this conclusion was reached are those 

 to which I have alluded — the polished surfaces, rounded mate- 



