Dr. FiTTON on the Strata below the Chalk. 279 



Ft. In. 

 i. " Clay," dark muddy blue altogether about ] 1 



At top containing Terebratulse and Gryphites. 

 About 2 feet from top, a bed of Oslrea deltoidea. 

 At 4 feet from top, a second bed of the same. 

 About 7 feet, Ammonites and several small bivalves. 

 In some places Belemnites, at the lower part. 



5 " Rock;" reddish yellow sandy limestone : — (^Oxford oolite). 



(147.) Oxford Oolite. — The section No. 18' shows the manner in which 

 this group comes in, after the gault and green-sand, on the great road from 

 London ; and the transverse section, Plate X b. fig 10., further explains its 

 relation to the Portland stone and sands, which, in the eastern part of Sec- 

 tion 18' are either wanting, or concealed by a prolongation of the gault and 

 green-sands. The Oxford oolite is seen, in the transverse section, to rise 

 from beneath the heights, towards the west of north, at an angle of about 9°; 

 and it is probable that all the strata here, from the Portland downward, decline 

 more to the south than the chalk and the upper members of the series : they 

 seem to form the southern slope of a curve or saddle, the opposite side of 

 which would descend towards the north, somewhere between Wheatley and 

 the Brill-hill range. The lower beds here are much harder than the rest ; 

 they consist of sparry limestone, including oolitic grains, and the masses are 

 blue in the middle : I obtained from them an O^trea ; Terebratula media ; 

 Melania IJeddingtonensis ; and a Spongia. 



(148.) Section, PI. X. a. A^o. 19. From the chalk, through Thame and 

 Long Crendon, to Brill and Muswell Hill. — The characteristic of the sec- 

 tion on this line, is the distinctness with which the Portland sand is exhibited, 

 almost throughout its course. The suj)erior strata are best seen in the 

 quarries around Brill, and at some points on the ridge between that place 

 and Long Crendon. 



The tract on the north and east of Chinnor, on the line thence to Thame, has very obviously 

 been at one time the bottom of a sea or lake, over which the chalk impended as a lofty shore ; 

 and near which the tides or currents acted witli such uniformity as to level down the ridge of the 

 lower green-sand; — while on the west, the ranges of Brill, Qiiainton, Whitchurch, and other less 

 prominent summits, stood out as banks or islands, at a short distance from the land. These re- 

 lations are all very well seen from the ground about Barley Hill, on the north-east of Thame. 



Gault. — At a point on or near the section, between Black Ditches Hill, Cotmore Walls, and 

 Sydenham-hurst, a well had been sunk forty feet, and then bored to fifty more, entirely in tough 

 dark blue clay, beneath which was sand rock. 



Lower Green-sand. — In a great number of the quarries in this part of the country, the ferruginous 

 sands at the upper part are separated from the rubbly stone beneath, by dark tough clay, 4 to 9 

 inches thick, which follows the irregularities of the mass below, and coats the bottom of cavities 

 like the "Gulls" of Hazeley, (p. 276.). The stony matter seems to be either the " Malm" of 

 Garsington and Combe Wood, or the representative of some other portion of the Purbeck series. 

 VOL. IV. SECOND SERIES. 2 O 



