234 ON THE FOSSIL ICHTHYOSAURUS, 



of lime, the residue being alumina and oxide of iron, which give the 

 mortar prepared with this lime the important property of hardening 

 under water. It is a marine formation ; and, besides the bones of 

 Ichthyosauri and of other saurian animals, it abounds in the re- 

 mains of fishes, crustaceous animals, and mollusca, particularly of 

 gryphiEte and ammonites ; and fragments of carbonized and pyritous 

 wood are frequently found, both in the stone and clay. Parts of 

 the strata constituting the Lias are much impregnated with bitu- 

 men, so as to have led to their being worked for coal ; and where 

 this occurs in conjunction with pyrites, as at Whitby, vast quanti- 

 ties of alum are procured from the decomposition, by spontaneous or 

 artificial con^bustion, of these substances. From the great regularity 

 and evenness of the beds of stone and clay, whose inclination is not 

 more than forty feet in a mile towards the south-east, as well as 

 from their nonconformity with the new red sandstone, it is evident 

 that this was in a quiescent state at the time that the Lias was de- 

 posited over it ; and the general absence of fragments of rocks or 

 stones in the Lias strata would lead us to the conclusion that this 

 formation also was the result of causes acting, not with violence, 

 but continuously, did not certain circumstances connected with the 

 distribution and state of preservation of the organic remains, tend 

 to induce a belief that catastrophes, of sufficient force not only to 

 cause the death of the inhabitants of the deep, but also to produce 

 their speedy interment in the mud and oose at the bottom, were 

 not of unfrequent occurrence at this period. 



The Lias at Barrow-upon-Soar, in Leicestershire, where the pre- 

 sent specimen was found, presents a remarkable regularity and cor- 

 respondence in the thickness of the layers of limestone and clay, the 

 former being usually ten inches, the latter eighteen inches, thick. 

 The dip is but slight, amounting only to an inch in a yard to the 

 east, although Mount Sorrel, a sienitic rock and the first of a range 

 of primary rocks extending over the forest of Charnwood, is in the 

 immediate vicinity, being only separated by the little stream of the 

 Soar and the meadows through which it flows, from the out- crop of 

 the Lias on the opposite bank. 



The nodule that contains the Ichthyosaurus, however, did not lie 

 in one of these beds of stone, but in a stratum of reddish clay above 

 them. When entire, it was nearly six feet long and two feet wide, 

 and about seven inches thick, having the general form of a fish 

 deprived of its tail. It was broken into several portions by remov- 

 ing it from the quarry, and the parts containing the end of the nose 

 and part of the tail were lost. It is formed of a series of concentric 



