Physical Geography. 165 



being the natural marine successors of these strata on 

 the Continent of Europe, are in like manner the natural 

 marine successors of the lake-formed sediments of the 

 red Keuper marls, and in reality are true passage 

 beds from those red marls into the Lower Lias ; and a 

 candid consideration of the fossil fish, reptiles, shells, 

 insects, and plants of the British Khsetic strata 

 strengthens this view. When the waters of the old 

 lakes were invaded by the sea, a migration of a few 

 marine forms took possession of the old lacustrine area, 

 and this depression gradually proceeding, culminated 

 in the development of the great Liassic fauna, at a time 

 when the old continent was submerged, and the moun- 

 tain tracts were converted into groups of islands, the 

 shores of which were washed by a broadening Liassic 

 sea. 



