Ch. xil] on the juea. 149 



angular blocks of granite, gneiss, and other crystalline formations, came 

 from the Alps, and that they have been brought for a distance of 50 

 miles and upwards across one of the widest and deepest valleys of the 

 world, so that they are now lodged on the hills and valleys of a chain 

 composed of limestone and other formations, altogether distinct from 

 those of the Alps. Their great size and angularity, after a journey of so 

 many leagues, has justly excited wonder ; for hundreds of them are as 

 large as cottages ; and one in particular, celebrated under the name of 

 Pierre a Bot, rests on the side of a hill about 900 feet above the lake 

 of Xeufchatel, and is no less than 40 feet in diameter. 



It will be remarked that these blocks on the Jura offer an exception 

 to the rule before laid down, as applicable in general to erratics, since 

 they have gone from south to north. Some of the largest masses of 

 granite and gneiss have been found to contain 50,000 and 60,000 cubic feet 

 of stone, and one limestone block at Devens, near Box, which has travelled 

 30 miles, contains 161,000 cubic feet, its angles being sharp and unworn.* 



Von Buch, Escher, and Studer have shown, from an examination of 

 the mineral composition of the boulders, that those on the western Jura, 

 near Neufehatel, have come from the region of Mont Blanc and the 

 Valais ; those on the middle parts of the Jura from the Bernese Ober- 

 land ; and those on the eastern Jura from the Alps of the small cantons, 

 Glaris, Schwytz, Uri, and Zug. The blocks, therefore, of these three 

 great districts have been derived from parts of the Alps nearest to the 

 localities in the Jura where we now find them, as if they had crossed 

 the great valley in a direction at right angles to its length : the most 

 western stream having followed the course of the Rhone ; the central, 

 that of the Aar ; and the eastern, that of the two great rivers, Reuss 

 and Limmat. The non-intermixture of these groups of travelled frag- 

 ments, except near their confines, was always regarded as most enig- 

 matical by those who adopted the opinion of Saussure, that tbey were 

 all whirled along by a rapid current of muddy water rushing from the 

 Alps. 



M. Charpentier first suggested, as before mentioned, that the Swiss 

 glaciers once reached continuously to the Jura, and conveyed to them 

 these erratics ; but at the same time he conceived that the Alps were 

 formerly higher than now. M. Agassiz, on the other hand, instead of 

 introducing distinct and separate glaciers, suggested that the whole valley 

 of Switzerland might have been filled with ice, and that one great sheet 

 of it extended from the Alps to the Jura, when the two chains were of 

 the same height as now relatively to each other. Such an hypothesis 

 labors under this difficulty, that the difference of altitude, when distributed 

 over a space of 50 miles, gives an inclination of no more than two de- 

 grees, or far less than that of any known glaciers. It has, however, since 

 received the able support of Professor James Forbes, in his excellent work 

 on the Alps, published in 1843. 



* Archiac, Hist, des Progr&s, &c. vol. ii. p. 249. 



