824 Blocks of'orhicidar''GrdnitiB-<iistQVerklin 



rest on nny solid foundation :and it would he c'ntire1y'r(^f?i^tt} 

 iF tht smooth bUwks, alluded to bv M. Mathieu, discovered 

 within the spare oF 400 square metres, instead of having 

 been wont or smoolked by the ejfi'claof decomlX)ntiort'j ha3; 

 been so worn by the action oF soiiie violent convulsion' <^f 

 the sea at ven^ rei«ote periods, when these blocks as (4ell 

 as that at Talavo mut^t have been transported to *th'e fyl'ace^ 

 where they were discovered. We see many exauTples, 

 even on very high niouutains, of these accidental transports* 

 of masses much more numerous and much larger, •(^f'gfa-; 

 nites and other rocks not less hard, all the angles of uhich 

 havebeen flattpnedby frictions. Besides, those in- the 'ei^vi- 

 rons of Saitene ^fe at a trifling height, and of shia(ll sizt^v 

 in comparisoni.wiih' the enormous fnasses mentioned by 

 Saussure in his Travels in th6 Alpsy -and whiG-h-heconsille'r^ 

 as the result of What he calls lagrande d^badte^ ■' ^''' '^^''» 



We are certainly far from wishing to lessen in the smalls-' 

 est degree the merit of M. Mathieu's Memoir, to whom. 

 we are under great obligations for conrmunicating the dis-^ 

 covery ; but we insist the more strongly on a new exathina- 

 tion of the smoothed blocks of Sartcne^ as the precise 

 knowledge which we have of that of Talavo, which has- 

 never been smoothed by decomposithn, but by friction, leads 

 us by analogy to consider the blocks in question as being' 

 the result of a similar cause : — for nothing could have less^ 

 tendency to decomposition than the orbicular granite of 

 Talavo, the block of which was very hard and very sound 

 internally, as well as on the external surfaces, which last 

 did not bear any other signs of destruction than that pro- 

 duced by shocks or by friction. 



We must therefore invite M. Mathieu to examine again 

 with attention the state of the blocks which he mentions 

 in his Memoir, and to ascertain positively, First, If they 

 really were smoothed by the effects of decomposition P Se- 

 condly, If these blocks are adherent, or separated from ther 

 granite rock on which they rest i which is not clearly enough 

 described in his Memoir. And finally. If semitransparent 

 quartz exists, as he says it does, in the new orbicular granite t 

 for the old piece is devoid of it, and is composed Only of 

 semitransparent feldspar, and aiT}philx)le of a greenish black, 

 with a little mica, which is only met with rarely and m 

 small spots. 



XXXIX. Pro- 



