FOSSILS IN STONESFIELD SLATE. 



187 



Purbeck beds, which, however, properly belong to the Wealden for- 

 mation described in the next chapter. Between the Portland and 

 Purbeck limestone, there is a bed of dark earth, called the dirt-bed, 

 in which roots and stumps of trees occur, sometimes erect, proving 

 that this bed was once dry land, and the soil on which the plants grew. 



It would not be compatible with the plan of the present work, to 

 enter into a detailed description of the numerous beds in this great 

 formation : they present general features of resemblance, both in 

 their characters and fossils. There is one bed, however, which is so 

 remarkable for its extraordinary organic remains, that it merits the 

 particular attention of the geologist. This is the Stonesfield slate in 

 Oxfordshire, before mentioned : it is now regarded as an undoubted 

 member of the oolite series, comprised in the forest marble of the 

 lower division. 



The Stonesfield slate consists of two beds of yellowish or greyish 

 oolitic limestone, each about two feet tliick, and separated by a bed 

 of loose calcareous sandstone about the same thickness. The Stones- 

 field slate, on exposure to frost, divides into thin plates, which are 

 used for roofing. The stone is obtained by working horizontal gal- 

 leries in the hill, which galleries communicate with deep perpendicu- 

 lar shafts. It is to be regretted, that no account has been yet pub- 

 lished of the different strata of stone sunk through by these shafts, 

 as we might hence derive decisive evidence, respecting the true geo- 

 logical position of the Stonesfield slate. 



The fossil remains in the Stonesfield slate consist of the impress- 

 ions of the outer cases or elytra of winged insects, and the bones of 

 small animals of the opossum or didelphis genus, and also the bones 

 of the megalosaurus or gigantic lizard, supposed to be analogous to 

 the Monitor. From the size of these bones, it is estimated that the 

 animal to which they belonged was forty feet in length and twelve 

 feet high. Legs and thigh bones of birds are also found in the 

 Stonesfield slate, with the teeth, palates, and vertebrae of fishes, and 

 two or three varieties of crabs and lobsters. Several varieties of 

 marine shells and of plants occur in the same beds. The most re- 

 markable circumstance attending these fossil remains, is, that they 

 should occur in strata which are generally believed to have been de- 

 posited before the creation of terrestrial mammalia. If, however, 

 there were islands, inhabited by the higher class of animals, when 

 the oolite beds were forming, their bones may have been carried 

 down by rivers into the sea, and deposited with those of marine ani- 

 mals. But though this hypothesis might satisfactorily explain the 

 occurrence of these remains in the Stonesfield slate, it would still be 

 not less extraordinary, that similar remains should have been no 

 where found in any of the upper secondary strata in England, nor in 

 other countries ; and that they are never met with, except in strata 

 considerably above the chalk formation. The occurrence of wood, 

 and beds of lignite, (or wood coal,) in oolite, confirms the opinion 



