L 



A group of strata, whose order of 

 superposition is below the Purbeck 

 and above the lias : called also the 

 Jura limestone from the extensive 

 chain of the Jura mountains being 

 principally composed of lias and 

 the oolitic series. The two lowest 

 members of this group, or those 

 immediately above the lias, are 

 called the great oolite, and the 

 inferior oolite. All the members 

 of the group are marine deposites. 

 The oolite has been thus named 

 from its being composed of spherical 

 granular concretions, supposed to 

 resemble the roe, or eggs, of a fish : 

 it is a mere term of convenience, 

 like those of carboniferous, red 

 sandstone, &c., for many limestones 

 in other groups are oolitic, while, 

 on the other hand, this mineralogi- 

 cal character is found only in an 

 insignificant part of the rocks 

 known as the oolite formation in 

 England and France. The oolite 

 is an accumulation of sands, sand- 

 stones, marls, clays, and limestones, 

 ranging across our island from 

 Dorsetshire on the south-west, to 

 Yorkshire on the north-east. The 

 central members of this group 

 occupy the high districts of Oxford- 

 shire and Gloucestershire. A very 

 striking zoological feature of this 

 group is the immense abundance of 

 ammonites and belemnites which 

 must have existed previous to, and 

 during its deposit; for, notwith- 

 standing the usual chances of de- 

 struction to which we may suppose 

 they were exposed, myriads of 

 their shells have been found en- 

 tombed entire, and not unfrequently 

 the animal must have been in them. 

 One hundred and seventy-three 

 species of ammonites, and. sixty-five 

 species of belemnites have been 

 enumerated as discovered in the 

 polite. There can be little doubt 

 that this group, greatly expanded 

 in thickness, and mixed with sand- 

 stones, marls, and slates, possessing 



[ 325 ] L 



a very different aspect from the 

 equivalent rocks in a large portion 

 of Western Europe, extends over 

 various parts of Eastern Europe. 

 The aggregate average thickness of 

 the oolite may be estimated at 1200 

 feet. In some instances, the spher- 

 ical granular concretions, which are 

 imbedded in many of the strata, 

 attain the size of a pea, and this 

 variety has obtained the name of 

 pisiform oolite. Some oolites have 

 been used for building-stone, but 

 they are said not to be durable. 

 Somerset House is built of oolite. 

 The vertebrated animals, whose 

 remains are found in oolite, are 

 fishes and reptiles of the same 

 genera as those discovered in the 

 lias. Mammalia have been found 

 at Stonesfield in Oxfordshire, where 

 there are the remains of more than 

 one species of Didelphis. Ptero- 

 dactyles have been discovered at 

 Solenhofen (where there would 

 appear to be many species), at 

 Lyme Eegis, in Dorsetshire, and 

 at Banz, in Bavaria. Some strata 

 of this group are composed, almost 

 entirely, of madreporites, and these 

 have been called " coral ragg." 

 Other strata abound in the remains 

 of fossil alcyonia and sponges, and 

 with congeries of minute millepores 

 and madrepores. In England, the 

 limestone of the oolite has a yellow- 

 ish-brown, or ochreous colour, by 

 which it may at once be distin- 

 guished from the lias ; and the 

 fossils partaking of the colour of 

 the limestone, renders it easy to 

 separate them from the fossils of 

 the lias. The oolite has been 

 divided into three formations, the 

 upper, the middle, and the lower. 

 These formations, in England, 

 occupy a zone having nearly thirty 

 miles in average breadth, extend- 

 ing across the island from Yorkshire 

 on the north-east, to Dorsetshire on 

 the south-west. Between the lower 

 and the middle division of oolites, 



