Erratics of the A ZpafadO 299 



the upper extremity performing these functions — transporting boul- 

 ders, and polishing and striating the rocks in contact with it to the 

 height of 300 feet above the visible bottom of the valley. But in 

 the same valley, both at the present glacier and many miles lower 

 down, we find the same characteristic marks of glacier action ; at a 

 much greater elevation, we find large boulders, and these generally 

 angular, not rounded or water- worn, transported from the upper 

 valley and lodged on the sides of the lower at a height not much 

 short of 2000 feet, and we find polished and striated rocks at the 

 same elevation. Can we doubt that the same effects in both cases 

 proceeded from the same causes — that the agent which now deposits 

 boulders and polishes rocks at 300 feet of elevation, also deposited 

 the boulders and polished the rocks at 1700 or 2500 feet? — in a 

 word, that a glacier 2500 feet in depth at some former period oc- 

 cupied the valley of Hasli, and extended to Thun, or beyond it ? 

 Where the parallelism is so complete, it would be against all sound 

 philosophical principles to account for the phenomena by calling in 

 a different agency, and one, too, purely hypothetical, to supersede 

 that which is in operation before our eyes. 



■ ihied eil- tfo e djuoa orfo 



(.£52 .q t whis?& ans P ortat i' on of Alpine Blocks to Jura. 3I jj 970^ 



We have thus good evidence that glaciers like the present, but of 

 much greater dimensions, afford a satisfactory explanation of the 

 transference of granite blocks from the higher Alps to the lower ends 

 of the valleys in the limestone district — that is, to the borders of the 

 level country. It remains to be considered how far the same agency 

 will account for the transportation of blocks from the Alps across 

 the level country to Mount Jura. These blocks were long a puzzle 

 to geologists, and are still a marvel to tourists. They are of gra- 

 nite gneiss, and other rocks belonging to the Alps, and they are 

 seen lying in thousands on the southern face of the limestone chain 

 of Jura, to which they must have been carried across the plain of 

 Switzerland over a space of fifty miles or more. They are found 

 not merely at the foot, or on the lower declivities of Jura, but high 

 on its sides, at an elevation of 2000 feet above the country they had 

 traversed. The first hint of the theory which attributes the con- 

 veyance of the granite boulders to glaciers was given by our towns- 

 man the late Professor Playfair. It was afterwards broached by M. 

 Venetz, a Swiss engineer, who probably was not aware that his idea 

 had been anticipated. It was next adopted by Charpentier, who 

 fortified it with a great variety of evidence in a memoir produced in 

 1834, and republished in an enlarged form in 1840; and it has 

 received further support from Agassiz and Guyot of Neuchatel. 



Map II. represents the western portion of Switzerland, iooi 1o 

 ^ediG-, the Lake, and g, the Town of Geneva. sq 



B D, the Bernese Oberland. The Lakes of Thun and Brienz are 

 seen near D. 



