298 ORDERLY DISTRIBUTION OF ALPINE ERRATICS. CHAP. XT. 



great clearness before the British public in 1852 by Mr. 

 Charles Maclaren, who had himself visited Switzerland for 

 the sake of forming an independent opinion on a theoretical 

 question of so much interest and on which so many eminent 

 men of science had come to such opposite conclusions.* 



M. Guyot had endeavored to show that the Alpine erratics, 

 instead of being scattered at random over the Jura and the 

 great plain of Switzerland, are arranged in a certain deter- 

 nunate order, strictly analogous to that which ought to 

 prevail if they had once constituted the lateral, medial, and 

 terminal moraines of great glaciers. The rocks chiefly relied 

 on as evidence of this distribution consist of three varieties 

 of granite, besides gneiss, chlorite-slate, euphotide, serpentine, 

 and a peculiar kind of conglomerate, all of them mineral 

 compounds, foreign alike to the great strath between the 

 Alps and Jura, and to the structure of the Jura itself. In 

 these two regions, limestones, sandstones, and clays of the 

 seeondarj^ and tertiary formations alone crop out at the sur- 

 face, so that the travelled fragments of Alpine origin can 

 easily be distinguished, and in some cases the precise localities 

 pointed out from whence they must have come. 



The accompanying anap or diagram, slightly altered from 

 one given by Mr. Maclaren, will enable the reader mox-e 

 fully to appreciate the line of argument relied on by M. 

 Guyot. The dotted area is that over which the Alpine 

 fragments were spread by the supposed extinct glacier of the 

 Ehone. The site of the present reduced glacier of that name 

 is shown at a. From that point, the boulders may first be 

 traced to b, or Martigny, where the valley takes an abrupt 

 turn at right angles to its former course. Here the blocks 

 belonging to the right side of the river, or derived from c, d, e, 

 have not crossed over to the left side at b, as they should 



* Edinburgh New Philosophical Magazine, October, 1S52. 



