292 Dr. FiTTON on the Strata below the Chalk. 



Ft. In. 



3. Uniform, yellowish-grey sand; precisely resembling that which includes the stone! „ ^ 



called " Les Grises " in the quarries near Boulogne visible about / 



[Portland Sand.~\ 



4. Hard, dark brownish-grey stone, of irregular thickness, containing Pernae. Approach-! ^ . 



ing to the nodules of Shotover ) 



Bottom of the Quarry. 



5. Below is green matter, used to form the floors of barns ; not visible here at present, but 



well seen near Dunton. 



In a pit at Dunton, the equivalent of the bed 3. is only three feet thick ; and that of 4. consists 

 of rubbly calcaieous stone, alternating with sand, the whole full of green particles, with small 

 pebbles of black flint, — at the bottom of which is a continuous bed of greenish stone, about 2 feet 

 thick, with dark particles, containing large Ammonites, Perna quadrata, and many other fossils. 

 The equivalent of 5. is tough green matter, apparently the same with that which gives the greenish 

 hue to the stone. This has been dug to the depth of about 3 feet. 



Kimmeridge Clay. — This clay is sufficiently characterized, at several points near Aylesbury, 

 by its occurring immediately beneath the Portland sand, and by its fossils. On the north- 

 west of the town, towards Bierton, it appears beneath about five feet of brownish sandy clay,— 

 (Portland sand ?,) which includes numerous fragments of flint ; and it contains Septaria, with 

 Ammonites. The tiles made of it are of a full red colour. Thence to the entrance of Whitchurch 

 on the south, the road appears to be cut wholly in the clay : but there are variations in the hue of 

 the beds exposed along the road, and perhaps some alternating layers of sand. In descending to 

 the streamlet south of Hardwick, were iridescent fragments of shells, with Gryphcea {Exogyra) 

 virgula, (PI. XXIIT. fig. 10), and Aptychus, (PI. XXIII. fig. 11), in the ditches at the road-side. 

 At Quainton, clay forms the slope of the hill beneath the stone-pits ; and a well had been dug, at 

 the village, in clay, to the depth of 60 yards ; among the fossils brought up from which, were 

 beautiful specimens of Ammonites Gulielmi, like those obtained, along with A. hiplex, from East 

 Claydon, about three miles north of Quainton, where they were found about 20 feet deep in 

 clay. 



The clay-pits beneath the hill at Stewkley, about midway between that village and the Warren 

 above mentioned, also afford Aptychus, and Exogyra virgula ; with compressed Ammonites of the 

 Kimmeridge clay, and a species supposed to be new. 



(153.) Section No. '2,],— from Dunstable through Hockliffe to JVoburn; — 

 and No. 21', Hockliffe to Fenny Stratford. — The tract occupied by the strata 

 below the chalk, from Aylesbury to the coast of Norfolk, is even less known 

 geologically, than that between Buckinghamshire and the south-eastern coast; 

 the maps of Mr. Smith and Mr. Greenough, and the general description 

 of Messrs. Conybeare and Phillips being the only publications relating to it. 

 The want of correct maps would alone have prevented the complete examina- 

 tion of this district ; but this impediment will soon be removed by the com- 

 pletion of the Ordnance Survey from Bedfordshire to Cambridge. The fol- 

 lowing observations indicate only some of the more prominent facts connected 

 with the beds below the chalk. 



