212 EXCAVATIONS AT DEWLISH. 



MR. CLEMENT REID'S NOTES AND ANALYSES. 



In order to trace the source of the material filling the deep 

 pot-holes in the chalk, a number of samples were examined 

 under the microscope, with the result that the whole of the 

 material seems to have come from the existing catchment- 

 basin of the Devil's Brook. Most of the samples show a 

 highly calcareous sand, consisting to a large extent of minute 

 grains of chalk and chalk-dust. This is full of sponge- 

 spicules, broken foraminifera and entomostraca, with a 

 few fragments of bryozoa, echinoderms, and shells, all 

 apparently from the Upper Chalk. 



The insoluble residue left after treatment with weak acid 

 varies in most of the samples from 10 to 60%, the highest 

 percentage occurring in a fine-grained highly glauconite 

 sand found in the upper part of section I. In this particular 

 sample the amount of glauconite, the uniform size of most of 

 the quartz-grains and their coating with a film of iron-oxide, 

 not easily removed, suggest that the bulk of this material 

 comes from the Upper Greensand, which crops out about 

 three miles up the valley. But mixed with this rusty sand 

 is a smaller quantity of perfectly clear small grains of quartz 

 and a number of sponge-spicules not in any way stained. 

 The clear sand is probably from the Lower Chalk two miles 

 away, and the sponge-spicules and other fossils are from the 

 Chalk in the neighbourhood. 



Most of the residues show also a small number of larger 

 and more rounded sand-grains, coming from the Eocene 

 deposits in the immediate neighbourhood. This we should 

 expect, as sub-angular grit-stones from the Eocene occur 

 occasionally in the gravels, and Eocene outliers are still to 

 be found not far from Dewlish. 



Among the larger stones a considerable proportion, 

 especially of the broken flints, show a highly-polished surface, 

 where the flint is hard and sound, but a dull white surface 

 where the flint is white and porous within. Not all the flints 

 are thus polished, and only a few of the large flints ; but so large 



