Dr. FiTTON on the Strata below the Chalk. 295 



Nutfield described above (141.); which, however, is thicker than this of Bedfordshire, and is 

 continued through a much larger space. I did not find here any of those nodules of sulphate 

 of barytes, which are frequent in the earth of Nutfield ; and in neither of these two situa- 

 tions does this bed contain the great number and variety of fossils by which the Fuller's earth 

 at the bottom of the Lower green- sand is distinguished, at Atherfield in the Isle of Wight. In 

 the sands of this part of Bedfordshire silicified coniferous wood is frequently found in large 

 detached pieces. 



These pits have continued to supply Fuller's earth for more than a hundred years. They were 

 described, in 1723, by Dr. Holloway, in a letter to the celebrated Woodward, which is remarkable 

 in the earlier history of stratigraphical geology in England*: the author pointing out the paral- 

 lelism of the rano-e of sands, to that of the chalk in the Chiltern hills, and suggesting distinctly, 

 upon geological grounds, the probability that other portions of the sand range would afford the 

 same valuable material; which, we have seen, coincides with the result of modern investigation. 



The iunction of the Lower green-sand and the Kimmeridge clay at Little Brickhill, (Section 21 ' ; 

 occurs at the north-west end of the village, in the garden of a small public-house called the 

 King and Queen, on the south of the road. Copious springs break out on the road about 50 

 paces above this house. The clay, which is here of a dark blue colour, includes very fine spe- 

 cimens of an Ostrea deltoidea, with Belemnites ; and I was told that sand alternates with the 

 clay for a short distance below this point. 



(154.) North-east of Bedfordshire. — The Lower green-sand, according to 

 Smith's map, passes through the whole of this county, in a band which is in 

 g-eneral parallel to the chalk escarpment, and about five miles in width ; 

 but its apparent dimensions vary much, in consequence of the irregular en- 

 croachments of the gault over the surface ; that stratum, immediately on 

 the north of Section 21, extending northward from the little village of Heath, 

 through Potsgrove and Froxfield, to Steppingley and Flitwick. Again, on 

 the east of Ampthill, an insulated portion of clay, (the colour of which, in 

 Smith's map, is intended either for Gault or Kimmeridge clay,) stretches 

 in a north-eastern direction from around Maulden to South Hill, crossing the 

 great London road to Bedford, about the 43rd milestone. Since, however, 

 the full development of the Lower green-sand in Bedfordshire renders it 

 probable that the subdivisions of the Kentish coast may be found also in 

 this country, it may deserve inquiry whether some of these detached por- 

 tions, which have been considered as clay, — (especially between Maulden 

 and South Hill) may not belong to the middle, dark-coloured, and retentive 

 member of the sands ; and the same question may be applied to a part, at 

 least, of the remoter tract assigned by Smith to the Gault, on the north of 

 Hockhff. 



* This document has been inserted in Conybeare and Phillips's "Outlines", p. 138-9. Dr. 

 Woodward himself speaks almost poetically of the value of the English Fuller's earth ; which, he 

 says, is beyond that of the Diamond mines of Golconda, &c. : — Edinb. Rev. 1819, vol. xxix. ; 

 and London and Edinb. Phil, Mag. 1832, vol. i. p. 155. 

 VOL. IV. SECOND SERIES. 2 Q 



