CHAPTEE XV, 



THE LIAS. 



Lias of English ; Calcaire a Gryphites of French ; and Gryphitenkalk and 

 Jura-kalk of German Authors. 



MUSEUMS : British Museum, those of Scarborough, Whitby, of Viscount 

 Enniskillen, Sir P. Egerton, Professor Sedgwick, and those of Dorsetshire, 

 Yorkshire, and the Midland Counties. 



AUTHORS : Buckland, Conybeare, Phillips, De la Beche, Murchison, Roemer, 

 Koch, and Dunker. 



CHARACTERISTICS : A Marine deposit, chiefly remarkable for the remains 

 of enormous Reptiles, principally of the Genera Ichthyosaurus and 

 Plesiosaurus. 



THE English provincial name lias has been very gene- 

 rally adopted for a formation of argillaceous limestone, 

 marl, and clay, which forms the base of the oolite, and is 

 classed by many geologists as part of that group. They 

 pass, indeed, into each other in some places, as near 

 Bath, a sandy marl called the marlstone of the lias being 

 interposed, and partaking of the mineral characters of the 

 upper lias and inferior oolite. These last mentioned 

 divisions have also some fossils in common, such as Avicula 

 incequivalvis. 



Nevertheless the lias may be traced throughout a great 

 part of Europe as a separate and independent group, 01 

 considerable thickness, varying from 500 to 1000 feet, 

 containing many peculiar fossils, and having a very uniform 

 lithological aspect. Although usually conformable to the 

 oolite, it is sometimes as in the Jura, unconformable. Thus, 

 in the environs of Lons-le-Saulnier, for instance, the strata 

 of Has are inclined at an angle of about 45, while the 

 incumbent oolitic marls are horizontal.* 



The peculiar aspect which is most characteristic of the 



* Sir C. Lyell, Elements of Geology, First Edition, page 386. 







