402 PETRIFACTIONS AND THEIR TEACHINGS. CHAP. IV. 



fossils imbedded in its slaty limestones, as we had occasion to 

 observe when describing the remains of the Megalosaurus, in 

 the previous chapter. In crossing the country from Oxford 

 to Stonesfield, the Oxford clay, so rich in Ammonites, Belem- 

 nites, &c. is first observed ; this deposit is succeeded by the 

 Cornbrash, 1 the uppermost stratum of the Great Oolite group, 

 which is seen beneath the clay in several quarries on the 

 road-side between Woodstock and Blenheim. 



The village of Stonesfield is situated on the brow of a valley, 

 both sides of which are deeply excavated by the shafts and 

 galleries that have been constructed for the extraction of the 

 laminated oolitic limestone, or slate, as it is locally termed. 

 The beds that supply the stone are at a depth of about fifty 

 feet below the summit, and are worked by shafts. The upper 

 twenty-five feet consist of clays alternating with calcareous 

 stone ; the lower, of fine-grained oolitic limestone abounding 

 in casts of marine shells, among which a small species of 

 trigonia is conspicuous. The strata that are worked do not 

 exceed six feet in thickness, and consist of rubbly stone, with 

 sand imbedding concretional masses of laminated grit, which, 

 by exposure to the frost, admits of easy separation into thin 

 flakes or slabs, that were formerly in general use for paving 

 and roofing ; like the slaty limestones of the Weald of 

 Sussex. 2 



The abundance of the remains of terrestrial plants, of rep- 

 tiles, and of land insects, in the Stonesfield strata, associated 

 with the usual marine shells, &c. of the Oolite, proves the 

 fluvio-marine origin of these deposits : in other words, this 

 assemblage of terrestrial and deep-sea exuviae indicates that 

 these strata were formed in the bed of an ocean, into which 

 the remains of the animals and plants of the neighbouring 

 lands were transported by currents ; while the fresh-water 

 shelly limestones of the Wealden, together with the absence 

 of marine species, equally demonstrate the fluviatile origin 

 of that formation. Referring the reader to the " Wonders of 

 Geology " 3 for a full consideration of the interesting questions 



1 See Table of Formations, ante, p. 5. 



2 See " Wonders of Geology," p. 508, for an abstract of Dr. Fitton's 

 account of the Stonesfield slate. 



3 Sixth Edit. Section V. pp. 507512. 



