184 



ORGANIC REMAINS. 



clusively to the oolite formation : in the magnesian limestone, and 

 even in transition limestone, a tendency to an oolitic structure may 

 be sometimes observed. It is not yet ascertained, whether these 

 globules are the result of a tendency to crystalline arrangement, or 

 whether they are of animal origin. 



The organic remains that occur in the different beds of oolite are 

 so numerous and various, that it would require an ample volume to 

 describe them fully. It will, however, be necessary to notice those 

 fossil genera that differ remarkably from the genera whose remains 

 are found in the lower strata, and indicate a considerable change in 

 the condition of the globe, or at least in those parts of it where the 

 strata were deposited. 



It has been already observed, that most of the shells in the lower 

 strata are different species with internal chambers, such as nautilites, 

 ammonites, and belemnites, and that univalve unchambered shells 

 are rarely found among them. By far the greater number of genera 

 that have left their remains in these strata belong to the acephalous 

 Mollusca, or such as had neither heads nor eyes, and inhabited bi- 

 valve shells. Even in the lias, only about five genera of spiral uni- 

 valve unchambered shells have been well ascertained, and the num- 

 ber of species or of individual shells is small. In the oolite, the ge- 

 nera and species of univalve unchambered shells are more numerous, 

 and the individual shells of several species abound in some of the 

 strata. Now, as these animals had heads and eyes, and moved on 

 their bellies like the land-snail, we may infer, that they did not live 

 in deep seas, where the sense of vision could not be available ; they 

 lived apd moved in comparatively shallow water near the shore. 



The vertebrated animals, whose remains are found in oolite, are 

 fishes and reptiles of the same genera as those discovered in lias ; 

 some, undoubtedly, belong to the crocodile genus, and had feet, like 

 the living species of crocodiles ; hence we may infer, that there were 

 dry land and rivers in the vicinity. 



It may well excite surprise, that calcareous strata should so rarely 

 be found, which present distinct indications of having been formed 

 exclusively by coralline polypi ; particularly as coral rocks and reefs, 

 of great extent, are so rapidly forming in our present seas. There 

 are, however, among the strata of oolite, some, which are composed 

 almost entirely of madreporites, and have received the name of coral 

 ragg. There are other strata which abound in the remains of fossil 

 sponges and alcyonia, and with congeries of minute millepores and 

 madrepores. More than twenty species of trochiform or top-shaped 

 spiral shells, and several species of echinites, are found in the oolite 

 strata ; but in the has below, as before stated, only a few genera and 

 species occur, and the individual shells are scarce. The gryphcea in- 

 cyrvttj so common in the lias, is rarely if ever found in the oolite 

 strata ; but another species, with a broad expanded shell, called the 

 gryphcea dilatata, is a fossil frequently found in different beds of the 



