Essay introductory to Geology. 7 



" his 'prentice hand " in various preliminary experiments on simpler 

 structures. 



But how little countenance all this will derive from geological research, 

 must be obvious from the slightest consideration of the foregoing catalogue : 

 that list is indeed confined to marine animals. Tliough vegetable remains, 

 which must have been derived from considerable terrestrial forests, prove 

 that dry continents must already have reared their heads above the waves j 

 and it may seem little agreeable to the analogy of all that we can observe 

 of the regulations of providence to suppose, that these continents should 

 have been left untenanted by appropriate animals, yet this subject must 

 always remain mysterious ; and although we should incline to suppose 

 that sucli terrestrial animals may tlien have existed, it will not be very 

 difficult to account for the non-discovery of their remains in tracts which 

 must tlien have been 'only part and parcel of the "dark nnfathomed 

 deptlis of ocean." But although thus confined to marine genera, we 

 can find no trace of less perfection of organic structure in those races than 

 in their actual successors in similar situations : if we consider separately 

 each order of animals, we do not find the simplest forms of that order in 

 the oldest rocks, and these progressively growing more complicated and 

 perfect in the succeeding geological periods j quite the reverse, we have 

 from the very first the crinoidea, by far the most complicated forms of the 

 echinodermata ; the cephalopoda, which are at the head of the molluscaj 

 and vertebrated fish, which appear to have been quite as perfect as their con- 

 geners, the sharks of the present day. The forms are different indeed, but 

 it does not appear that they are inferior; and if we consider the immense 

 step there is between the simplest forms of animal life, and a structure like 

 that of any of the verlebrata, a shark for instance, such as occurs in these 

 fossiiiferous beds, it must be obvious that the interval between the latter 

 and the most perfect of tlie mammalia is comparatively so very trifling as 

 to be quite incommensurable. 



To proceed to the next, or secondary order of fossiiiferous beds, including, 



1. The poecilitic groupe, so called from the variegated, or new red sand- 

 stone, which is intimately associated with the magnesian limestone, or 

 zechstein, as its lowest member; and, in its upper part, with the muscliel- 

 kalk of the continent, (a formation which does not occur in this island.) 



2. Tiie three divisions of oolites, reposing each on a thick argillaceous de- 

 posit, of which the lowest is the lias ; these oolites are separated from the 

 next groupe in the weald of Kent by a large formation of fresh water, sand, 

 and limestone ; but this has not yet been noticed elsewhere. 3. The ere - 

 taccoi's groupe, consisting of chalk reposing on green sand ; the latter being 

 subdivided into upper and lower. 



The fossils throughout this groupe bear strong generic resemblances, 

 although, as might be naturally expected, the extreme terms, viz. the 

 magnesian limestone below, and the chalk above, exhibit a gradual ap- 



