227 



CONTEIBIJTIONS TO THE GEOLOGY OE GLOUCESTEKSHIRE. 



THE LIAS. 



Er xnE Eev. P. E. Beodie, M.A., E.G.S., Sec, kc. 



( C'onti.m'.ed from page 8S.) 



It is one of the many striking facts of geology that, as we pass from 

 one great group of rocks to another, "we find a considerable change both 

 in lithological and zoological characters. Sometimes the transition is 

 abrupt and sudden, at others, slow and gradual. In the former case, 

 the marine fauna of the older deposit had perished, and a new race 

 sprung up and succeeded to its place ; while, in the latter, there was 

 only a gradual dying out of some species unable to exist under the 

 changed oceanic conditions, others more hardy still continuing 

 to flourish in the later formation. Eut this change of genera and 

 species is not confined necessarily to the breaks which seem to have 

 taken place between one great rock-system and another ; it is often to be 

 noted in a greater or less degree, as we have seen in our review of the 

 Oolites in this count}^, in the minor divisions and sub-divisions 

 of each formation. The student must also bear in mind that the 

 strata which form the crust of the globe were, for the most part, 

 deposited by the sea; a very small proportion only being the 

 products of fresh water, and still fewer being purely terrestrial. 

 Therefore, in our researches into the history of the past, wo have 

 to deal more usually with the varied inhabitants of the ancient 

 seas, and to mark the changes which took place from time to lime 

 as we pass through either entire periods, or the parts and details 

 into which they may be divided. If we could walk along the bed of 

 the ocean, and look vrith admiration and awe on the wonderful and 

 beautiful creatures which people its depths and its shallows, we 

 should know more their living history, their habits, and their 

 structure, than we do ; and many a supposed fact would have to be set 

 aside, and many a lesson would have to be learnt, perhaps, by the 

 very wisest amongst us. Many, then, will hear with surprise (if they 

 hear it for the first time) that the ground on which they tread once 

 formed the bottom of the sea — perhaps at some dark, unfathomable 

 depth inhabited by strange, uncouth monsters, v/hich have no repre- 

 sentatives in the present age. He who wishes to study the records of 

 past creations has the sea-bottom at his feet, as it were, and can 



