Prof. Struder on Bowlders. 325 



Art. V. — Translations relative to Bowlders a7id Cobalt Ores, 

 from the Neues Jahrhuch fur Mi?ieralogie, Geognosie, Geolo- 

 gic und Petrefaktenkunde, herausgegeben von Dr. Leonhard 

 und Dr. Brown. Jahrgang, 1838. Rev. W. A. Larned. 



I. On the Recent Explanations of the Phenomenon of Erratic 

 Blocks ; by Hr. Prof. B. Struder. 



The wish expressed in yonr last letter of publishing in the 

 Jahrbuch, my geological remarks upon the recent explanation of 

 the phenomenon of erratic blocks, is the occasion of the following 

 communication. 



After all the endeavors, observations, and speculations of the 

 last ten years, we see the phenomenon of erratic blocks still veiled 

 in a mist, which hinders us from taking a full and exact view of 

 them, and which has not as yet permitted a general elucidation. 

 Hence we are disposed to view every new theory with favor, and 

 we overlook at first its difficult points, though they may be not a 

 few, because of the satisfactory explanation of others, on which 

 we have hitherto labored in vain. 



The floating or forcing of bowlders by powerful currents of 

 water, still appears to me, to afford the explanation, which best 

 agrees with the facts, although at the same time I confess that I 

 am not prepared with an entirely satisfactory answer to several 

 admitted and recent objections. In order to hold up the blocks 

 while floating from the Alps to the Jura, we suppose instead of 

 streams of pure water, streams of mud and detritus, without being 

 able fully to show what became of this smaller rubbish. In order 

 to carry them over the deep Swiss lakes or the Baltic Sea, we 

 assume a kind of lateral impulse, while we make the avulsion of 

 the blocks cotemporaneous with the rise of the mountain and the 

 sinking of the sea: but, it is clear from examinations in Switzer- 

 land, that the spread of the blocks must have been later than the 

 formation of the present molasse-vallies,* which however we 

 deduce from the last heaving process of the Alpine range ; that, 

 moreover, in the later epoch of the molasse formation, the sea in 



* Molasse is a term, descriptive of a soft green sandstone, occurring throughout 

 the lower country of Switzerland. — Lyell, Principles of Geology, Vol. 4, p. 75. — Tr. 



