274 Dr. FiTTON on the Strata below the Chalk. 



graduates upwards also into the Portland sands. He supposes, therefore, that certain beds of 

 the series are wanting between the freestone of the Headington quarries and the incumbent 

 Kimmeridge clay ; an inference confirmed by the condition of the surface of the freestone, — 

 which Mr. Conybeare describes as exhibiting the appearance of having been marked by the 

 action of water upon it, before the deposition of the clay ; " presenting occasionally small cup- 

 " shaped cavities, and per|)endicular rents of various breadth, into which the clay had insinuated 

 " itself*." It is not, however, improbable that some of the intermediate strata exist on the line 

 of section from Garsington to Langcombe. See hereafter, p. 278. 



Oxford Oolite {Coral Rag of Smith). — The characters of this group have been described by 

 Mr. Conybeare. Its general course is nearly conformable to that of the upper strata, and is 

 represented in Mr. Smith's and Mr. Greenough's maps. On the east of Islip a narrow inter- 

 rupted ridge passes north-eastward, for about nine miles from Woodeaton, as far as Stanhill near 

 Marsh Gibbon, and is separated from the escarpment of the Portland stone and sand at Muswell 

 Hill (Section No. 19.), by a uniform flat, apparently occupied by clay. Blackthorn, a place upon 

 the ridge, affords a bluish oolite, which Smith refers to the Coral Rag. This ridge appears to 

 separate the Kimmeridge from the Oxford clay ; but the continuity of the former so far westward 

 from Muswell Hill, where it ascends considerably, implies a thickness much greater than that 

 in the Headington quarries. 



The regular course of the Oxford oolite is interrupted by the offset mentioned in the last page, 

 which extends a little eastward of its general direction to Wheatley (see the Transverse Sec- 

 tion, PI. X. b. fig. 10.) ; the strata there rising towards the north, at an angle of about 9°. The 

 previous dip about Garsington is much less ; and that of the general range of this formation in 

 Oxfordshire, according to Conybeare f, not more than 1°. Tliis upheaving seems to be continued 

 eastward for some miles, so as to bring up the Portland sands at a point much closer to the 

 chalk near Thame, than on the north-east of that place. 



(144.) Section PI. X. a. No. IS,— frotn the Chalk through Hazeley, Gar- 

 sington, and Shotover,to Oxford ; — and No. l8'.Jro7n Stokenchurch, through 

 Tetsworth, to Wheatley. — The upper strata between the Gault and the 

 Portland stone on the hne of Section 18^ are best seen near the summit of 

 the range from Combe Wood to Shotover Hill : and I am indebted to Mr. 

 Hugh E. Strickland, for the following account of the ferruginous sand at 

 that place, which I have not examined myself. 



Shotover Hill : — \_Lower Green-sandy and Wealden.'] 



" The bed which crowns the hill and rests on the supposed equivalent of the Portland stone, 

 " consists of a series of sands, mostly ferruginous, but frequently assuming various shades of 

 " yellow, white, grey, and even black, according to the proportion of oxide of iron which they 

 " contain. The sand occasionally graduates into marl and clay ; and seams of yellow ochre also 

 " occur, which afford considerable supplies of that article. The stratification of the sands and 

 " marls is often very tortuous and irregular, which seems rather to be owing to the circumstances 

 " of iheir deposition, than to any subsequent action. In some cases the oxide of iron has been 



* Outlines, &c., p. 189. -f- Ibid., p. 192. 



