116 SCIENCE IN SHORT CHAPTERS. 



But this negative anomaly is not all. The ancient gla- 

 cial deposits are not only remarkable on account of the 

 absence of the most characteristic of modern glacial de- 

 posits, but in consisting mainly of something which is quite 

 different from any of the deposits actually formed by any 

 of the modern glaciers of Switzerland or any other country 

 within the temperate zones. 



I have seen nothing either at the foot or the sides of any 

 living Alpine or Scandinavian glacier that even approxi- 

 mately represents the "till" or "boulder clay," nor any 

 description of such a formation by any other observer ; and 

 have met with no note of this very suggestive anomaly by 

 any writer on glaciers. Yet the till and bowlder clay form 

 vast deposits, covering thousands of square miles even of 

 the limited area of the British Isles, and constitute the 

 main evidence upon which we base all our theories respect- 

 ing the existence and the vast extent and influence of the 

 "Great Ice Age." 



Although so different from anything at present produced 

 by the Alpine or Scandinavian glaciers, this great deposit 

 is unquestionably of glacial origin. The evidences upon 

 which this general conclusion rests are fully stated by Mr. 



but that there is another moraine adjoining it, or in continuation 

 with it, which is covered with vegetation, and stretches quite across 

 the mouth of the valley. The Duke of Roxburgh, who is well ac- 

 quainted with this neighborhood, having spent sixteen summers in 

 Arctic Norway, was one of our fellow-passengers, and told me that 

 this moraine forms a barrier that dams up the waters of a considera- 

 ble lake, abounding with remarkably fine char. I learned this just 

 as the packet was starting, too late to go on shore even for a few 

 minutes, and obtain a view of this lake and the valley beyond. This 

 I regret, as it might have revealed some explanation of the excep- 

 tional nature of this moraine. It would be interesting to learn 

 whether it belongs to the greater ice age, or to that period of minor 

 glaciation that fashioned the farm patches already described. The 

 formation of the lake is easily understood in the latter case. It is 

 only required that such a minor reglaciated valley as one of these 

 should be of larger magnitude and of very gentle inclination at its 

 lower part, so that the secondary glacier should die out before reach- 

 ing the present seashore. It would then deposit its moraine across the 

 mouth of the valley, and this moraine would dam up the waters 

 which such a valley must necessarily receive from the drainage of its 

 hilly sides. Llyn Idwal, in North Wales, is a lake thus formed, 



