92 Reports and Proceedings — Geological Society of London,. 



from the Chalk. Of late years the opinion has been growing that 

 it consists very largely of material derived from the Eocene. 



The present paper is devoted to an examination of the facts, 

 with the view of ascertaining whether the Clay-with-FIints could 

 possibly be derived from the Chalk, or whether the theory of its 

 derivation from the Eocene is confirmed by more detailed enquiry. 

 The author first describes its composition, noting that unbroken 

 flints are not everywhere abundant, that broken angular flints are 

 common, and green-coated flints are not rare ; finally, that if the 

 clay is washed it always yields a residue of sand, composed chiefly 

 of rounded quartz - grains with some of iron - oxide, and both 

 apparently derived from the Eocene sands. 



The thickness of the accumulation is next discussed, especially 

 with reference to sheets of it that lie on fairly even floors. In such 

 positions it varies from 2 to 12 feet in depth, and large areas occur 

 where it must have an average depth of 3 or 4 feet. The products 

 resulting from artificial solution of chalk are then considered, and 

 a series of analyses is given, from which the average amount of 

 insoluble residue existing in the four lower zones of the Upper 

 Chalk is deduced. Experiments have been made by Mr. Williaih 

 Hill to determine the related weights of a cubic foot of Upper 

 Chalk and a cubic foot of Clay-with-Flints, in oi'der that allowance 

 might be made for the diifereuce in calculating the quantity of clay 

 which would be left by the solution of a given quantity of chalk. 

 The result shows that 100 cubic feet of the Micraster coranguinum 

 Chalk will produce only 1*2 cubic feet of clajf, and the solution of 

 the Marsupites and Micraster coranguinum Zones to the extent of 

 200 feet over any part of the area would only yield clay enough to 

 make a layer 2 feet deep. Lastly, it is shown that the quantity of 

 flints in the Upper Chalk is so much greater than the quantity of 

 clay that the natural residue could not form a Clay-with-Flints. 

 Thus, solution of 100 feet of Micraster coranguinum Chalk would 

 yield a bed of flints about 7 feet thick, and only enough clay to fill 

 up the interstices between the nodules. 



The next section is devoted to the distribution of the Clay-with- 

 Flints, and its stratigraphical relations to the Chalk on the one hand 

 and to the Eocene on the other. In dealing with this part of the 

 subject, details ai'e restricted to the areas lying west and north-west 

 of the London Basin and to the wide area between the Loudon and 

 Hampshire Basins. 



From these several lines of investigation the author concludes :— 

 (1) That the Clay-with-Flints cannot have been formed from mere 

 solution of the Upper Chalk ; (2) that all its components, except 

 the unbroken and angular flints, could have been furnished by the 

 Reading Beds; (3) that the positions occupied by it are such that 

 no great thickness of Chalk can have been desti'oyed to form it, 

 the tracts being seldom more than 30 or 40 feet below the local 

 plane of the Eocene base, or the presumed level of that plane. 



Finally, an attempt is made to explain the manner in which the 

 Clay-with-Flints was formed, and the theory adopted is that the 



