436 ON THE GEOLOGY OF THE 



are fresh-water shells ; the third, which is of a large size when 

 compared with the others, is of the exact form of B. Ampulla 

 of LiNNiEus, or Amygdalus of Dillwyn, a marine shell. 

 That these may have fallen accidentally into fissures, and 

 have been there conglomerated in the process of time, is 

 quite possible ; but their occurrence at such an elevation be- 

 speaks an order of things totally different from that which pre- 

 vailed at a subsequent period. I shall only further observe; 

 with respect to the brescia itself, that it is wonderful to see how 

 completely and perfectly the upfilling has been accomplished^ 

 Instead of the pores being choaked, through which the fluid 

 must have passed from the surface to the interior of the rock, 

 the liquid seems to have been absorbed as if by a sponge, and 

 the mass presents very often a greater degree of solidity in the 

 interior than towards the surface. — I shall now proceed to the 

 Second Limestone. 



This variety rests upon the first ; and in this neighbour- 

 hood is composed of strata very various in their dimen- 

 sions, measuring from a few inches to two and three feet 

 in thickness. It may even exceed this, but not frequent- 

 ly. In this diversity in the dimensions of its strata, it pre- 

 sents a strong contrast with the First Limestone, whose 

 beds are found to be remarkably uniform, when we have 

 favourable opportunities of seeing them displayed. It is ac- 

 companied occasionally with a poor species of clay-ironstone, 

 and a kind of blue marly clay, a substance which is very much 

 o-iven to decompose. Although it rests upon the first lime- 

 stone, it does not maintain a conformable position : it seems 

 as if it had been deposited immediately before the hills had 

 assumed their present forms, and as if by means of their ab- 

 rupt elevation, to have been thrown aside previous to its per- 

 fect consolidation, into the valleys in the most complete con- 

 fusion, 



