70 Rev. 0. Fisher — The Coprolite Pits of Cambridgeshire. 



Neither rain- wash nor river-action, even if a river were at hand, 

 could have eflfected this. 



It almost always occurs in this neighbourhood that, when the 

 coprolites are near the surface (say at a depth less than three feet), 

 they undulate rapidly, the depressed parts of the bed being thickened. 

 When they get so near the surface that the crests of the undulations 

 are cut off by the trail, and the depressions alone remain, they are 

 said to be " pocketty," and the pockets seem to contain almost the 

 entire store of coprolites, as if the whole of the stratum had been 

 accumulated in the depressions. 



The following section was taken in the same pit as the two former. 



Fig. 5. — Scale ^-inch to a yard. 

 W. Section showing Pockets. E. 



[a) Warp. (6) Trail. (c, c, c, c) Pockets containing Phosphatic Nodules respectively 2 ft., 

 2 ft., 14 ft., and 1 ft. deep, [d) Gault. 



It must not, however, be supposed that the undulations are long 

 troughs, though I think it may be asserted that there is a general 

 parallelism about them. They are rather, as they are termed, 

 " pockets," although I think they are usually longer in one dimen- 

 sion, and that in the same direction for all. Here I think we have 

 another consequence of lateral pressure. 



I have one more instance of the transference of material in an 

 unscattered state to mention. It occurs near Lords Bridge Station. 

 A ditch was dug some time ago upon my glebe, and I observed 

 beneath the gravel covering, and resting upon the Gault, a portion of 

 the coprolite bed, with a little of the white clay above it. I thought, 

 upon seeing it, that I had discovered a bed of coprolites which might 

 be worked ; but, upon examination, it turned out to be an isolated 

 patch of a very few yards in length, forming a portion of the trail. 

 It is evident it must have travelled in a mass to its present position. 



I have published my opinion that land-ice may have been instru- 

 mental in producing the condition of the surface^ which I have 

 described ; and I have given reasons for supposing that the climate 

 of these latitudes may have been sufficiently rigorous for that result 

 about 100,000 years ago.^ It appears to me that a sheet of ice, 

 moving over the surface, would disturb it to a depth depending 

 partly upon the pressure and partly upon the nature of the material. 

 Between the ice and the solid earth there would be a layer of 

 material of a certain thickness interposed, which had been entirely 

 detached from the rock, constituting what is called a moraine 

 profonde. 



I conceive the trail to be a remnant of it, thinned off by subse- 

 quent atmospheric denudation, which has derived the warp from it. 



1 Geological Magazine, Vol. III., p. 483. 2 jj/^.^ yoi. lY., p. 193. 



