172 THEORY OF THE EARTH. 



the most solid and most ancient formations, and on 

 the other, with the recent alluvial depositions made 

 by the Po, the Arno, and their tributary streams ; 

 as also, to determine their relations with the innu- 

 merable masses of volcanic productions which are 

 interposed between them ; and, finally, to ascertain 

 the mutual situations of the various sorts of shells, 

 and of the fossil bones of elephants, rhinoceroses, 

 hippopotami, whales, cachalots, and dolphins, in 

 which several of these hills abound. I have only 

 a very superficial knowledge of these lower hills 

 of the Appenine chain, acquired in the course of a 

 journey devoted to other objects; but I am of 

 opinion that they contain the true secret of the last 

 operations of the sea. 



There are many other strata, even celebrated 

 for their extraneous fossils, which have not been 

 hitherto so accurately examined as to enable them 

 to be connected with the general series, and whose 

 relative antiquity, therefore, has not been ascer- 

 tained. The copper slate of Thuringia* is said 

 to be filled with the remains of fresh-water fish, 

 and to be older than most of the secondary or 

 floetz formations. We are also as yet uninformed 

 of the real position of the stinkstone slate of Oen- 

 irigen, which is also said to be full of the remains 

 of fresh-water fish ; of that of Verona, evidently 

 abounding in the remains of sea-fish, but which 



* Bituminous marl slate. Jameson's Mineralog3 r , vol. ii. p. 1 97. 



