Essay introductory to Geology. 3 



sive formations also abounding in objects of the most interesting curiosity 

 to the philosopliical observer of nature, namely, various relics of the 

 organized structures of vegetables and animals imbedded in tlie solid rocks; 

 a large proportion of these remains are marine shells, and at once force 

 liome on the mind the obvious conclusion of the Roman poet : — 

 " Vidi factas ex tequore terras, 

 Et procul a pelage conchae jacuere marinse." 



But our attention is not claimed by these organic remains solely on account 

 of the striking fact of their occurrence in such situations, but still more by 

 the very important circumstance that more than nine-tenths of them are 

 of species altogether dift'erent from those which we at present'find in exist- 

 ence, and in many cases even the very genera have vanished from the face 

 of nature. The number of species of corals, echinodermata, and testaceous 

 mollusca, known only in a fossil state, nearly rival in number the whole of 

 the actually existing species;* the fossil fish are almost equally important. 

 The class of reptiles presents us with many extinct monsters, some of 

 which supply links which have subsequently dropped out and been lost 

 from the great chain of nature, exhibiting in one instance (the Ichthyosau- 

 rus) a gradation from the ordinary structure of saurians to that of fishes ; 

 and in another (the, Pterodactylus) a similar passage from saurians to birds. 

 'J'he fossil remains of mammalia, though confined to the most recent and 

 superficial deposits, still present very generally extinct species, and in 

 several instances extinct genera. Similar remarks will equally apply to 

 the genera and species of vegetables preserved in a fossil state, which are 

 in a majority of instances extinct. 



Barely to mention these facts, must sufficiently evince that no ])erson 

 who is unacquainted with the vast supplements which Geology thus affords 

 to Zoology and Botany, can be considered as adequately informed on those 

 iuterestiug departments of natural knowledge. 



The different series of formations differ very materially in the species of 

 organic remains which they include, and by whicii they are therefore said 

 to be characterised. Tlie species frequently vary from formation to for- 

 mation, so that tliey have been said, almost without exaggeration, to be as 

 regularly disposed in the geological formations, as in the drawers of a 

 well arranged museum ; hence if the fossils of any given locality be known, 

 we may securely pronounce as to its geological formation, and vice versa. 

 But although tlie species be generally distinct in distinct formations, yet 

 whole groupes and orders of formations arc related together by strong 

 generic resemblances as to their organic remains. 



• The splendid folio work of Goldfuss, now in tlic course of publication, and which 

 prornises to form the most complete ilkistration of organic remains ever given to the 

 world, has devoted nearly 100 large plates, each containing more than 10 figures, 

 to corals, echinodermata, and only two genera of bivalves, ostrea and pecten : — 

 hence some idea of the number of fossil species may be formed. 



