22 Missing Chapters of Geological History. 



But the Oolites are wonderfully rich in fossils in England, 

 and a careful tabulation of the species is more important in 

 them, because the number known is, no doubt, a much larger 

 proportion than usual of the whole. 



Excluding plants, there are nearly 1500 Oolitic species, of 

 which three-fourths lie in the lower Oolites, less than one- 

 fourth in the middle, and only about one-fourteenth part in the 

 upper beds. 



Although a considerable percentage of the upper Lias 

 species pass into the inferior Oolite, it must be understood that 

 this is an exceedingly small proportion of the Oolitic species. 

 In the older deposit (upper Lias) there are not more than about 

 seventy species, and in the newer (inferior Oolite) there are 

 almost five hundred. This much greater richness in species of 

 the newer deposit would be even more remarkable if we counted 

 individuals. In the upper Lias shales, fossils are compara- 

 tively rare, while the limestones of the inferior and great 

 Oolites are made up almost exclusively of them. 



Professor Ramsay gives a series of elaborate tables, pre- 

 pared with the help of Mr. Etheridge, showing the distribution 

 of species in the middle and newer part of the Secondary 

 epoch. The results are in the highest degree interesting and 

 valuable, and throw much light on the history of this remark- 

 able period, certainly one of those best illustrated, by its 

 deposits, of any that are known to geologists. For the pur- 

 pose at present under consideration, the result of a careful study 

 of these tables proves very clearly that no important paleeonto- 

 logical break takes place from the Lias to the Portland rock, 

 although during this time many species disappeared entirely, 

 and many more had been introduced ; some of these latter re- 

 placing others, which, however, so far as we can judge, must 

 have existed under precisely analogous conditions. Each forma- 

 tion in succession, as we pass upwards, contains a number of 

 species altogether new, mixed with a large number that have 

 already existed in the earlier formation. Of the common 

 species, some few pass through several formations ; some dis- 

 appear and re-appear, evidently owing to conditions tempora- 

 rily unfavourable. In some cases, as the Coral rag, the species 

 are more limited than usual. In others, as in the great Oolite, 

 there are unmistakeable indications of the vicinity of land. 



But, although there is no great break, there are sufficient 

 gaps to justify the assumption of many intervals and inter- 

 ruptions having taken place during the accumulation of the 

 middle Secondary rocks of England. Many deposits well 

 developed in one place, are absent in another. In some 

 places, as on the Dorsetshire coast, the sequence is perfect but 

 thin. In Yorkshire the lower beds are greatly modified, and 



