ON THE FOSSIL ICHTHYOSAURUS. 239 



in the bones, proving beyond a doubt that the bones were broken 

 while the enveloping matter was in a soft state, and that the flesh 

 or skin was in a great measure, if not entirely, removed. The com- 

 pressing force that produced these numerous dislocations and frac- 

 tures must have been considerable, and, supposing the animal's 

 body to have lain on its back or right side, passed in a direction 

 from right to left. 



As the present state of our knowledge of the mode in which the 

 Lias clays and limestones were formed, amounts to little more than 

 conjecture, it is not possible to give a satisfactory account of the 

 cause of the death of the Icthyosauri and other animals whose re- 

 mains are found in such a remarkably perfect state in that stratum; 

 but it is rather probable that, at Barrow at least, it may have been 

 owing to sudden changes in the temperature and other conditions 

 of the water, in consequence of volcanic action in the immediate 

 vicinity of that part of the primeval ocean. 



With regard to the nodular concretional form of the stone in 

 which the petrifaction is imbedded, an explanation may perhaps be 

 found by a reference to what has been observed to occur in the 

 mixture of Silex and Alumina with some Oxide of Iron, that forms 

 the potter's paste, which, when allowed to settle, begins to form 

 into lumps by the attraction of aggregation that the particles of 

 Silica have for each other. This circumstance has been applied to 

 explain the formation of flints in chalk ; and with the knowledge 

 of the property that the mortar made from Lias lime has to harden 

 under water, and of the tendency to form the same kind of concen- 

 tric nodules round any organic nucleus, so striking in the ironstone 

 beds of the coal measures, it need not be a matter of surprise that 

 similar nodules are developed in the Lias where the same ingredi- 

 ents meet together. 



The following analysis by Mr. Southall of this town, of the vari, 

 ous substances found in the fossil, shows decidedly that the process 

 of petrifaction has not entirely removed their animal matter. The 

 matters analyzed were the bones, the black matter that lay between 

 the ribs, and the white substance supposed to be coprolite. The 

 bones contain 'J') per cent, of matter soluble in diluted nitric acid, 

 and the residuum, which resembles ivory-black, yields, when heated, 

 an empyreumatic oil, and when a strong red heat is applied, the 

 greater part is consumed. JNIixed with oxymuriate of potash, the re- 

 siduum deflagrates in the same manner as a mixture of oxymuriate 

 and carbon. Ammonia added to a solution of the bones threw 

 down a copious precipitate ; and the nitrate of silver threw down 



