320 SKY. GEOLOGY. SECONDARY STRATA. 



gryphites ; a few small and smooth terebratulae being 

 occasionally found with them. Casts of ammonitse of 

 a large size are also to be seen ; but they are so imperfect 

 that I have never been able to procure a specimen 

 from which the description of the species could be 

 collected. Higher up, as it appears, in the order of 

 the beds, fragments of a small sulcated terebratula are 

 also to be found ; and still further on, large pectines occur 

 in considerable abundance, accompanied by fragments of 

 smaller shells so mutilated that it is impossible to refer 

 them to any known genera. 



From such remains, geologists have in many cases 

 successfully determined the analogies and relative po- 

 sitions of strata ; but they seem at the same time to have 

 expected from them a more perfect demonstration than, 

 in the present state of our knowledge, they are calculated 

 to afford respecting the succession of strata and the 

 different species of animal remains that occur in them. 

 However worthy of confidence these distinctions may be 

 in cases like those of the English strata, where a regular 

 order over an extensive space is found to exist, it is 

 not as yet safe to transfer the same criterion to detached 

 deposits like the present ; since the occasional absence 

 of some, and the partial nature of many strata, added 

 to our imperfect knowledge of fossil species, materially 

 interfere with the use of this test. With respect to the 

 rock under review, as it holds the nearest place to 

 the primary strata, it is thus far analogous to the moun- 

 tain limestone of the English. Yet this is not a proof 

 of its identity, since the inferior strata of the secondary 

 rocks are often wanting. If again we compare it with 

 the lias of the same geologists we shall find it to differ 

 in some important particulars from that rock, which \\ill 

 hereafter be shown to occur in this island with very 

 unquestionable characters ; nor is the nature of its organic 

 remains sufficient in the present state of our knowledge 



