184 PICTURESQUE SKETCHES 



but frequently changing both in depth and in the 

 nature of its deposits ; the islands being the habita- 

 tion of land animals, while the surrounding coasts af- 

 forded food and shelter for vast multitudes of fishes 

 and other marine groups. The marine deposit, how- 

 ever, seems to have been nearly limited towards the 

 west by a recently formed lias coast, leading us to 

 suspect the existence of land extending westwards 

 and northwards from the line of that bed. Possibly 

 this land may have formed a broken ring surrounding 

 a Mediterranean Sea, just as the two portions of the 

 great continent of America, connected partly by the 

 Isthmus of Darien, and partly by the chain of the 

 West India islands, now enclose a tract under nearly 

 similar conditions. 



However this may be, the great eastern oolitic 

 archipelago seems to have been limited towards the 

 west by England, and perhaps terminated towards 

 the north with the land which now forms the range 

 of the Hartz mountains, the mountains of Saxony, 

 and those of Bohemia. Throughout the whole tract 

 the general conditions of deposit must have been 

 nearly analogous ; but there were many important 

 modifications in detail, especially in the western, 

 southern, and south-eastern part, where the older beds 

 are most developed ; while in the north-eastern and 

 central districts, the newer beds are apparently the 

 most important. The newest of all the deposits was 

 a great fresh- water formation known as the Weal den 

 group, occupying a portion of the south-east of Eng- 

 land, and met with again in Hanover. 



By a gradual change in the nature of the deposits, 

 the whole oolitic range seems to have served as the 



