W. WHITAKER Otf THE RED CRA.G. 123 



iron-sandstone, which were often found to contain impressions and 

 casts of the shells that had been dissolved out ; and these, as far as 

 could be told, were of Crag species. They occur in the area in 

 which the sand has been thought to be unfossiliferous ; and I believe 

 they have not been described before from thence ; but in a paper 

 read to the Society in 1874 I have noticed like impressions of shells 

 near Sudbury and Hadleigh *. 



Absolute proof, however, of the correctness of the explanation 

 advanced was got by the observation of a few sections in which 

 the lines of bedding, or even of false-bedding, in the shelly Crag 

 were continued into the sand without shells. In some cases a 

 marked gravelly layer was clearly seen to be at one spot in the Crag 

 and at another in the sand ; and in one pit a hand-specimen could 

 be got of such a bed, half containing the actual shells, and the other 

 half with casts only. In some pits large masses of shelly Crag are 

 to be seen quite surrounded (in section) by the shelless sand — a fact 

 difficult of explanation on any other view, but comparatively easj T to 

 understand as brought about by irregular dissolving action, checked in 

 places by local hardness or slight decrease of permeability in the beds. 



In many cases the dissolving away of the shells would seem to 

 have been followed by some destruction of the lines of deposition in 

 the sand ; and, indeed, we should expect such a thing to occur on 

 the abstraction of so much material. It is, of course, in these cases 

 that the appearance of erosion is most deceptive. 



It may be asked " What becomes of the carbonate of lime of the 

 shells?" Some of it is doubtless carried away in the water of the 

 many springs from the bottom of the Red Crag, thrown out by the 

 London Clay beneath ; but in places some of it is again deposited 

 in the lower beds of the Crag as whitish marly streaks in slight 

 fissures or open spaces. Very possibly, however, great part of the 

 dissolution of shelly matter may have taken place under conditions 

 somewhat different from those we now see, when perhaps the Crag 

 was more permeated by water, or even water-logged. 



Small as this subject may be, yet it is, I think, worthy of notice, 

 and for three reasons : — because it tends to simplify our classifica- 

 tion over an important Crag tract ; because it shows a grenter ex- 

 tension of the Red Crag than has been thought to exist, that deposit 

 occurring in its almost unfossiliferous condition some way beyond 

 where it is known in its shelly state ; and because it draws atten- 

 tion to that slow metamorphism which takes place in permeable 

 beds through the agency of water, whether as a dissolver of car- 

 bonate of lime &c, or as a depositor of iron-oxides. 



Postscript. 



After this Note was read, I heard from M. E. Yanden Brock, of 

 Brussels, that he had observed an irregular junction of shelly and 

 shelless . sand, like that above described, in Belgium, and that he 

 attributed it to the same cause as that now suggested. 

 (For the Discussion on this paper see p. 140.) 



* Quart. Journ. Geol. Soc. vol. xxx. pp. 403, 404. 



