M. Studer on the Geological Structure of the Alps. ICl 



a mode of getting rid of the difficulty, and yet it would not 

 be easy in the present state of our knowledge to find a less 

 daring solution. 



Diluvium and Erratic Blocks. — The surface of the molasse 

 valleys and of the Swiss plain is covered by a bed of gravel 

 and of sand which sometimes attains a thickness of more than 

 100 feet ; this is the diluvium. In its nature, this deposit 

 corresponds exactly with the deposits brought down by the 

 torrents of the Alps. The predominating rocks are lime- 

 stones and Alpine sandstones, mixed with rolled masses of 

 nagelflue. The pebbles are always rounded, but rarely at- 

 tain the size of a man's head. It is in this diluvium, and even 

 deeper than it, that the present rivers have hollowed out their 

 beds. The superimposed terraces indicate alternations of 

 the epochs of repose and of activity. 



These large masses of gi^avel are covered by a more recent 

 diluvium, generally unstratified, containing large and small 

 pebbles, which are both round and angular, and also blocks of 

 several fathoms in diameter, imbedded in a sandy clay. The 

 largest blocks are sometimes isolated, sometimes united in 

 groups ; the one series rounded and blunted, notwithstanding 

 their large size, and the other more or less angular. This re- 

 cent diluvium sometimes abuts against the molasse hills, and 

 sometunes forms dykes or elongated hills from 20 to 100 feet 

 high, generally running parallel to the foot of the slopes or 

 following a transverse course in the valley. The only differ- 

 ence observable between the blocks of this recent diluvium 

 and true erratic blocks, is that the latter are isolated and free, 

 whereas the first are imbedded in the sand or the gravel. 

 There is a striking resemblance between the dykes formed of 

 transported materials and the descriptions given us of the 

 Osars'^ of Sweden. Now, if the glacial theory, according to 

 which some celebrated geologists believe that this phenomenon 

 ought to be explained, be really, of all the hypotheses hitherto 

 proposed, that which harmonizes the best with facts, the same 

 theory, in my opinion, ought to be applicable to the pheno- 

 menon presented by Sweden. 



•^ Osars, to which the attention of the geologists was first directed b/ 

 M. Alexander Brongniait, are long lines of transported materials having 

 the form of dykes or banks generally running N.N.E. and S.S.W.-— E. 1). 



VOL. XXXIII. NO. LXV. JULY 1812. L 



