Dr. FiTTON on the Strata below the Chalk. 273 



crop of the stone and sand, can be traced along a very irregular line, from the heights at Gar- 

 sington and Shotover, by Brill and Muswell Hills, Ashendon, Waddesdon, Quainton, and Whit- 

 church, to the points last mentioned, near Stewkley, which seem to be their limit in this direction. 



The Portland- sand goes out beyond the stone, on the north and north-west sides of the heights 

 just mentioned. The sand is in some places loose, grey, and yellowish ; but in general it abounds 

 in green particles, and is often almost wholly composed of green matter : the bluish half-concreted 

 mass, intermediate between stone and sandy clay, which is the predominating component of this 

 stratum on the coast, being here of rare occurrence*. Near the bottom, the sand includes 

 great nodular concretions of hard greenish grit, like those of Swindon, Shotover, and the Lower 

 Boulonnois ; and it contains sometimes worn, polished, fragments of very dark-coloured chert or 

 flinty slate. 



The Portland stone and sand are found between the principal ranges of Brill and Whitchurch, 

 (Sections 19. and 20.), and nearly at the same level, in the heights of Ashendon, Lodge Hill, 

 Chearsley, Over-Winchendon, Coney Hill, Cuddington, Dinton, Stone, and Hartwell. But on the 

 north-east of the road from Aylesbury to Winslow they are rarely visible, being deeply seated, 

 and concealed, especially in the vicinity of Leighton Buzzard, by large accumulations of gravel. 



The intermediate and lower tracts between the lines of section and the heights above men- 

 tioned appear to be occupied by clay, and the whole district is in general undisturbed ; no 

 derangements at least, at all comparable to those of the Wealden tract, or of the Dorsetshire 

 coast having yet been observed within it: but in many of the Portland quarries the beds of stone 

 are traversed by fissures, produced by violence long antecedent to the present condition of the 

 surface. An elevation comparatively inconsiderable, but analogous to that which has raised 

 the anticlinal ridges of the south, occurs at Wheatley, between the range of Shotover and that 

 of Brill, — both of which are capped by nearly conformable strata of Portland sand and stone, 

 rising gradually to the north-west; while the beds of the Oxford oolite, which appear in the 

 village of Wheatley, on the main road from London to Oxford, rise more rapidly northward, 

 from beneath the stone and sands of Garsington and Combe Wood. (See and compare the Sec- 

 tions, PI. X, a. No. 18. and 18', and PI. X, b. fig. 10.) A small portion, therefore, of the space 

 between the heights of Shotover and of Brill may be occupied by an anticlinal ridge, or curve, 

 of Oxford oolite. 



Kimmertdge Clay. — This is found everywhere, in these sections, beneath the Portland sand; and 

 is conformable to the superior strata. It is best seen on the west of Shotover Hill, where the 

 series of the strata is complete ; but near Leighton it seems to come nearer to the Lower green- 

 sand; and in the descent from the village of Little Brickhill, (Section No. 20.) it appears within 

 a few feet of the sand, which forms the upper part of the hills there. 



The whole of this stratum is disclosed, on the line of Section No. 18, at Headington ; and its 

 characters there are described by Mr. Conybearef. It seems to increase in bulk in advancing 

 northwards, but does not anywhere attain the thickness which it exhibits near Weymouth, in the 

 Boulonnois, and near Scarborough. Its predominant fossil here is Ostrea deltoidea : near Ayles- 

 bury are found Gryphcea virgula, and Aptychus. 



Professor Sedgwick has remarked that on the south-east coast near Weymouth, some of the same 

 fossils pervade this clay, the mixed beds near Weymouth, and the oolite beneath them ; and it 



* Bluish stone, somewhat like that of the sands in Purbeck and Portland, is found near the top 

 of this formation, at Hartwell near Aylesbury, 

 t Outhnes, &c. p. 185. 



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