262 A. J. JUKES-BROWNE ON THE RELATIONS OF 



I will now proceed to describe the exposures visible in Bedford 

 and Bucks, which derive special importance from the fact that the 

 Cambridge coprolite-bed ceases to exist before we reach the western 

 boundary of the former county. 



§ 2. The Gault and Chalk-marl in Bedfordshire. — From Arlesey 

 (which is just north of Hitchin) as far as Barton (see Map, p. 259), the 

 Gault continues to be about 200 feet in thickness. The nodule-bed 

 above also preserves its usual height of 8 or 9 inches ; but the matrix 

 seems to become rather more clayey in this district ; the glauconite 

 grains are equally abundant ; and the pits near Shillington show the 

 usual section in the following form : — 



Sandy marl or clunch, passing down into greyish green sandy clay with 



coprolites. 

 Stiff blue Gault containing a few coprolites, which are externally of a light 



colour. 



The surface of the clay is very uneven, and the coprolites are accu- 

 mulated in the hollows. Fossils appeared to be rather scarce, Avicula 

 gryphoioides, Terebratida biplicata, and teeth of Otodus being the 

 most common. The bed, however, is clearly of the Cambridge type. 

 The next noteworthy exposure is between the villages of Barton 

 and Sharpenhoe, about four miles south-west of Shillington. Here 

 the section is as follows : — 



ft. 



5. Greyish white marl 2 



4. Greenish grey marl with a few buff-coloured coprolites 4 



'6. Bluish clayey marl 2 



2. Bluish grey sandy clay with many fossils and coprolites = Cam- 

 bridge bed 1 



T. Blue clay or Gault 200 



The surface of the Gault was only slightly undulating ; and I was 

 told that in one part of the pit there was a second and lower vein of 

 coprolites about 10 inches thick, and separated from the main bed 

 by 3 or 4 inches of stiff blue clay, but that it eventually thinned out 

 and ran into the higher bed, thus suggesting the idea that a nodule- 

 bed of the Gault came to the surface here. 



Bed no. 2 seems to be the representative of the Cambridge Green- 

 sand ; but its appearance is very different, and most of the coprolites 

 are formed of a lighter- coloured phosphate, though some are of the 

 usual black colour; these latter, however, have not been subjected 

 to the same amount of rolling as those in Cambridgeshire, the small 

 Ostrece and Plicatulce upon them being in much better preservation, 

 and fine striations being visible on the latter, which I had never seen 

 before. In some parts the bed consisted of an aggregation of small 

 nodules cemented together into a kind of pudding-stone, which is an 

 occasional condition of the seam in the Cambridge pits. 



Some of the buff-coloured nodules, which were softer and more 

 easily worn in the mill, probably originated in this bed or in no. 4 ; 

 but others, as well as the dark coprolites, are more likely to have 

 been washed out of the passage-beds between the Gault and Chalk 

 described below. 



