724 



GEOLOGY 



Cuvier, in his great work, pro- 

 nounces these flying reptiles the 

 most extraordinary of all the 

 beings whose ancient existence 

 is revealed to us ; and those 

 which, if alive, would seem most 

 at variance with living forms. 

 Eight species have been deter- 

 mined, from the size of a snipe 

 to that of a cormorant, occurring 

 in the lias of Lyme Regis, the 

 oolite of Stonesfield, the grit of 

 the Wealden, and on the continent 

 at Pappenheim and Solenhofen. 

 The annexed cut exhibits the 

 chief reptiles of the liassic age, 

 the ichthyosaurus and plesio- 

 saurus, the latter in the act of 

 catching a pterodactyle. 

 Oolitic Group. The series of rocks which pass under this denomination have small 

 globules imbedded in them, resembling minute eggs or the roe of a fish, and hence the 

 generic name roestone or oolite, the latter term being a compound of the Greek wo*>, an 

 egg, and Xidoc, a stone. But this structure does not prevail through the entire formation, 

 nor is it exclusively confined to it, though sufficiently prominent to become character- 

 istic. Upon microscopic examination, the egg-like grains of these rocks are found to 

 consist either entirely of lime, or of calcareous accretions around some organic substance 

 as a nucleus, generally the fragment of a coral or a shell. The group comprehends, 

 beside the proper oolites, various alternating cla^s, sandstones, marls, and limestones, and 

 may be subdivided as follows : 



Restorations of Saurians and other Animals of the Lias. 



Upper. 



Portland stone. 

 Kimmeridge clay. 



Middle. 

 Coral rag. 

 Oxford clay. 



Lower. 



Cornbrash and forest marble. Fuller's earth- 



Great oolite and Stonesfield slate. Inferior oolite. 



The rogenstein or roestone of the Germans, the terrain jurassique of the French, consti- 

 tuting the great mass of the Jura Mountains, and various other continental deposits, 

 answer to the members of the series as developed in England. The oolitic group is 

 remarkable for the vast amount of calcareous matter which it contains, for its limestones 

 extensively employed in architecture, and for the great number and variety of its organic 

 remains^ The strata have variously a brown, light yellow, or grey tinge, derived from 

 the oxide of iron, according to the proportion in which it has been dispersed through 

 the mass. 



In the lower division of the group we have six members enumerated. The cornbrash 

 is a thin bed of coarse loose limestone, so called in Wiltshire, probably from the facility 

 with which the superincumbent red soil yields to the plough. The forest marble is a 

 fissile arenaceous limestone, frequently a congeries of dark-coloured shells, capable of 

 being polished, and hence occasionally worked as a marble, deriving its name from that 

 circumstance, and from its occurrence in Whichwood Forest, Oxfordshire, appearing also 

 mother localities. The great oolite, the most important member of the whole series for 

 thickness and utility, is a stratified calcareous mass, furnishing an excellent freestone, the 

 material of St. Paul's Cathedral, which was quarried near Burford, in Oxfordshire. It 



