J. D. Dana — Arnold Guyot 369 



lively band of friends established on the glacier of the Aar, in 

 order to learn the results of their doings and communicate his 

 own to them."* 



Switzerland in the ice-period was his subject ; and the 

 sources of the bowlders and the courses of ice-transportation 

 were the chief enquiries. The investigation involved excur- 

 sions on foot and careful examination over the whole range of 

 the Swiss Alps, the slopes into Italy, the plains of Switzerland, 

 and the mountains on the northern and western borders, in- 

 cluding the Juras — in all an area of 190 by 310 miles — in order 

 to trace the erratics to their high sources among the snowy sum- 

 mits, examine the rocks of ail peaks, ridges and valleys for 

 comparison with those of the erratics, measure the heights along 

 the lines and limits of the erratics from plain to mountain peak, 

 and note all glacial markings. The task was accomplished 

 with the greatest possible fidelity ; thousands of barometric 

 measurements were made in the course of it, and from 5000 to 

 6000 specimens were gathered in duplicate. 



Thus, says Guyot : 



Eight erratic basins were recognized on the northern slope of 

 the Alps — those of the Isere, the Arve, Rhone, Aar, Reuss, Lira- 

 mat, Sentis, and Rhine ; and four on the southern slope — that of 

 the Adda including Lake Como, of Lugano, of Ticino including 

 L. Maggiore, and that of the Val d'Aosta. Moreover a question 

 left hitherto untouched — the distribution in each basin of the 

 rocks special to it, was minutely examined, and the final results of 

 all the laws observed in the arrangement of the erratic fragments 

 were shown to be identical with the laws of the moraines. This 

 identity, and the absolute continuity of the erratic phenomena 

 from the heart of the Alps down the valleys and beyond to the 

 Jura left no alternative but to admit the ancient existence of 

 mighty glaciers as vast as the erratic regions themselves, having 

 a thickness of over 2000 feet. 



Brief notes on his work were published in the Bulletin of 

 the Neuchatel Society of the Natural Sciences, for November, 

 1843, May and December, 1845, and January, 1847, f he 

 reserving the complete report for the second volume of Agassiz's 

 great work on glaciers. But, unfortunately, after the first 

 volume by Agassiz appeared at Paris, in 1847, there came the 

 revolution of 1848, which put an end to their plans. 



The study of the geological structure of the Jura Mountains, 

 in which he worked out the system in the flexures of the 

 strata and proved that it must have been produced by lateral 

 pressure, was another of Guyot's labors soon after his return to 



* Memoir of Agassiz, page 39. 



f The facts are well presented also, though briefly, in the second volume of 

 D'Archiac's Histoire des Progres de la Geologie, pp. 259-265. 



Am. Jour. Sci.— Third Series, Vol. XXXI, No. 185, May, 1886. 

 24 



