Dr. FiTTON on the Strata below the Chalk. 283 



6. Sand ; .^0 feet (at least). The top only is visible here, but in other pits nodules of 1 

 great size are scattered in it irregularly, close to the stone 5 J 



These nodules are distinctly seen at an adjacent place called Dropshot. They are 

 from 2 to 4 feet in length, and about 18 inches thick, and consist of large sub- 

 globular masses of hard, bluish green, sometimes highly calcareous, crystalline, grit, 

 (here called "Bluestone"), like that of the concretions at Shotover. In some 

 cases it is remarkable tliat they are flat at tiie top, while the form beneath is sub- 

 globular, (fig. 1. of the subjoined cut); pebbles of dark brown or black flint ad- 

 hering to the upper surface, in a gravel-like crust. They are sometimes traversed 

 by vertical cracks and veins, as in the quarries at Mont Lambert in the Boulonnois ; 

 and when broken, these exhibit flat surfaces, — as in fig. 2, which represents a large 

 nodule, inverted, to show the form of the lower side*. 



Fig. 1. Fig. 2. 



Ft. In. 

 30 





4 5 6 Feet. 



10 



Muswell Hill. 



This hill, which forms the extreme promontory of tliis range, was one of the principal Ord- 

 nance stations, and is 744 feet above the sea. The summit, I was informed, is composed of: — 



1. Lower green-sand. Reddish sand, including concretions of a dark brown ferruginous t 



conglomerate (" carstone"), which occurs also in large masses, and in thick beds, I 

 under a very reddish and ferruginous soil 8 ft. to J 



[The Portland stone appears to be wanting here.] 



2. Portland Sand, with green particles ; Pernae, Trigoniae, Sphaerae, &c. 



8. Kimmeridge clay : springs breaking out at its contact with the sands. No stone, I 

 was informed, occurs between this place and Blackthorn : that which is employed 

 in all the flat country on the south-west of the range, coming from Muswell Hill 

 and Brill. 



From Muswell Hill there is a fine view to the west and north-west, of the great plain occupied 

 by the clays ; and westward over Otmoor, which is crossed by a Roman road from Oxford to 

 Bicester. 



Oxford Oolite. — The stone of Blackthorn, about 3| miles west of Muswell Hill, is a variety 

 of oolite or pisolite, consisting of oolitic grains disseminated through sparry limestone of a bluish 

 colour. 



(149.) Section, PI. X. a. No. 20. — From the Chalk near Wendoter, 

 through Axfleshury and Whitchurch in Buckinghamshire. — The two great 

 roads from London into Buckinghamshire cut through the chalk, one by the 

 vale or defile of Amersham and Wendover, the other and more northern, 

 by the Vale of Berkhampsteadand Tring, the general altitude of which above 

 the sea is about 350 feet; that of the adjacent heights of the chalk rising to 



* Fig. 1. is intended to represent a vertical section of a concretional mass of stone imbedded in 

 sand; of a subglobular or kidney-like form below, but flat at the top. 



Fig. 2. is a sketch of another nodule, with a vein at right angles to the mass ; througli which 

 a part has been broken off". 



