227 
CONTllIBUTIONS TO THE GEOLOGY OF GLOUCESTERSHIRE. 
THE LIAS. 
Br THE Rev. V. B. Brodie, M.A., F.G.S., kc, ka. 
{C'onlhnted/rom page S8.) 
It is one of the many striking facts of geology that, as we pass from 
QUO great group of rocks to another, we find a considerable change both 
in lithologicul and zoological characters. Sometimes the transition is 
abrupt and sudden, at others, slow and gradual. In the former case, 
tlie 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 
onl}' 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. But 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 bo 
noted in a greater or less degree, as we have seen in our review of the 
Oolites in this county, 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 
pi-oducts of fresh water, and still fewer being purely terrestrial. 
Therefore, in our researches into the history of the past, we liave 
to deal more usually with the varied inhabitants of the ancient 
seas, and to mark the changes which took place from time to time 
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 with admiration and awe on the wonderful and 
beautiful creatures which people its depths and its shallows, wo 
should know more r>f their living histor}'', 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, unfatliomable 
deptli inhabited by strange, uncouth nionstcrs, which have no repre- 
sentatives in the present age. Ho who wishes to study the records of 
past creations has the sea-bollom at his feet, as it were, and can 
