ORGANIC REMAINS IN LIAS. 



181 



stime gentleman, measured nine inches in breadth.* The vertebrae 

 of the ichthyosaurus nearly resemble those of a shark, which enabled 



it to bend its tail with great facility, and assisted the motion of its 

 paddles, in propelling the body with great velocity through water. 

 The skeleton of the ichthyosaurus, as arranged by Mr. Conybeare, 

 is represented in the annexed cut. Of the ichthyosarus, several spe- 

 cies have been discovered. The plesiosaurus resembles the former 

 genus in many important parts of its osteology ; but its vertebrae have 

 a closer approximation to those of the crocodile ; they are only slight- 

 ly concave : its neck was longer than its body, and was composed of 

 thirty vertebrae, which exceeds the number of the cervical vertebrae of 

 the swan. (See the annexed cut.) Five species of plesiosaurius have 



been determined ; some of them were 20 feet in length. The bones of 

 both animals are found very commonly in the cliffs of lias at Lyme 

 in Dorsetshire, and on the southern bank of the Severn. The organic 

 remains in lias are chiefly, but not exclusively, marine. Bones of 

 the turde and crocodile have been discovered in lias : the fossilized 

 remains of terrestrial plants also occur in it. This proves that dry 

 land must have existed in its vicinity, at the period of its deposition. 



The lias formation extends, in a waving line, through England, from 

 near Whitby in Yorkshire to Lyme in Dorsetshire; at both its ex- 

 tremities it is fully developed, and presents similar features, namely, — 

 dark cliffs of blackish clay or alum shale, with a nearly flat floor of 

 lias limestone extending into the sea, forming a natural pavement, 

 on which the observer may walk secure, treading at almost every 

 step on the organic remains of the inhabitants of a former world, 

 disseminated through the rock. These animal remains are, gener- 



* Mr Johnson of Bristol has during many years, devoted much time and labour, 

 and has liberally expended considerable sums of money, in collecting organic re- 

 mains of these saurian animals ; and it is to the collection of these remains, in his 

 private museum, that we are principally indebted for the discoveries which have 

 been made respecting them. 



