356 SCATTERED BLOCKS OF GRANITE NEAR GENEVA. 



That these valleys were formed before the transportation of the 

 granite blocks, seems evident from the circumstance before stated, 

 that the blocks occur in groups, opposite to the embouchures of all 

 the Alpine valleys, that open into the great valley of Geneva. These 

 valleys or depressions, were therefore formed before the country 

 emerged from the ocean, not by the erosion of rivers, but by the ele- 

 vation and fracture of the beds on each side. The summits of the 

 mountains that border the present valleys may have directed the 

 course of the rush of water by which the blocks were transported. 

 The valley of the Arve, in the upper part has evidently been a lake 

 or series of lakes, originally formed by elevation and depression : the 

 waters have cut passages through the barriers of these lakes at a 

 subsequent period, and the river Arve has afterwards cut through 

 the deep mass of sand and rounded stones, that fill the bottom of the 

 lower part of the valley, from Bonneville, to the junction of the Arve 

 with the Rhine. The transportation of the granite blocks was pos- 

 terior not only to the original formation of the Alpine valleys, but also 

 took place at a later period than the deposition of the deep mass of 

 sand and rolled stones, that forms the bed of the lower part of these 

 valleys, for the blocks often rest upon it. Blocks of similar granite 

 may be seen in the lake of Geneva between that city and Thonon, 

 which indicate that this part of the lake has undergone no great 

 change, since these blocks were deposited. The transportation of 

 the granite blocks appears to have been effected suddenly ; but the 

 rounded blocks and sand at the bottom of the valleys, must have 

 been long subjected to the violent agitation of water. 



There are numerous instances of transported masses of rock, 

 scattered over our own island, and various parts of the continent, 

 but none of them appear so immediately to elucidate the enquiry 

 respecting the origin of valleys, as the granite blocks in Savoy and 

 on the Jura. Seated on the side of a mountain among a group of 

 these blocks (as on the Saleve, near Geneva ;) you may see, at the 

 same time, the distant rocks from which they were torn, the valleys 

 or depressions along which they have been trasported, and the orig- 

 inal situations on which they were deposited, and where they remain 

 and may probably continue till another revolution of the globe. By 

 whatever force the granite was torn from the nearly vertical beds of 

 the Alps, the same force, acting on the level secondary strata, might 

 tear offa large extent of surface and uncover the lower beds : this is 

 what is understood by a denudation. 



The geological student is requested to observe that though I have 

 denominated these transported masses of rock in Savoy, granite 

 blocks, because they are principally granite, yet blocks of the other 

 Alpine rocks are also frequently intermixed with them. 



