726 GEOLOGY. 



naturalists from the inspection of other remains. It has been called Phascolotherium 

 (pliaskolos, a pouch.) At a more recent period, the Purbeck beds of the Upper Oolite have 



yielded a great variety of similar remains. 

 The discovery of these marsupial relics in 

 the Stonesfield slate, is a proof, as Dr. 

 Buckland observes, that this order, instead 

 of being, as was once supposed, of more 

 recent introduction than other orders of 

 mammalia, is in reality the first and 

 most ancient condition under which ani- 



Jaw of the Fhascolotherium. 



mals of this class appeared upon our 



planet. According to the data at present obtained, it was the only type of 

 mammalian organisation before the tertiary era; and once existed in Europe at a 

 high northern latitude, though now restricted to the tropical parts of North and South 

 America, to New Holland, and the adjacent islands. At Solenhofen, in Germany, in 

 strata corresponding with the Stonesfield slate, similar organic remains are found. 



The middle division of the oolite includes the Oxford clay and the coral rag. The 

 former, a dark blue tenacious clay, has underlying subordinate beds of limestone, called 

 Kelloway rock, from being exposed near Kelloway Bridge, in Wiltshire. The clay 

 extends over a considerable portion of France, including the Jura, into Germany ; and 

 in England it ranges along the valley of the Isis in Oxfordshire, the Ouse in Hunting 

 donshire, and the Witham in Lincolnshire. In the latter locality, where it is known as 

 the fen clay, it has a considerable expansion and great thickness ; for in sinking for water 

 at Boston the stratum has been penetrated to the extent of 478 feet, at which depth a 

 thin bed of stone, perhaps the Kelloway rock, was met with. Shells are numerous 

 through this formation, and bones of the ichthyosaurus occur, though rarely, and of a 

 different species from those found in the lias. The coral rag, the groupe coralien of 

 French authors, is a limestone composed, in certain situations, chiefly of corals, as its 

 name indicates ; but, besides this, the formation includes subjacent beds of sand or grit 

 stone, resting on the Oxford clay, and a calcareous freestone overlying the coral rag. 

 This freestone, largely composed of the comminuted fragments of shells, is the material of 

 many of the noble buildings of Oxford, whose appearance now attests its easy destruc- 

 tibility, being liable to scale off in large flakes after a few years' exposure to the weather. 

 Vertebrae of the ichthyosaurus, several beautiful echinites, and various shells, such as 

 astarte elegans, occur in this part of the oolitic series. 



The upper division of the oolite includes the Kimmeridge clay and Portland stone. 

 The former, a stratum lying over the superior beds of the coral rag, 

 varies in its composition from a greyish tenacious soil containing 

 selenite, covered with oak-woods, in Wiltshire, where it is called 

 the oak-tree clay, to highly bituminous shales, which are burnt 

 for fuel, near Kimmeridge, on the coast of Dorsetshire, which gives 

 its name to the whole deposit. The remains of crocodilians have 

 been found in the Kimmeridge clay of Honfleur in France, and 

 that of Oxfordshire has yielded the jaws, teeth, vertebra, and 

 bones of the extremities, of a large marine reptile allied to the 

 plesiosaurus, described and named by Professor Owen the Plio- 

 Astarte elegans. saurus. The Portland stone consists of a series of beds of cal 

 careous and siliceous freestone, of no great thickness or extent, being chiefly con 

 fined to the county of Dorset, but highly valuable for architectural purposes, having 

 yielded the material of Somerset House, and of many of the public edifices of the 



