14 



" The following observations have led me to infer that this bed is due to 

 the decomposition of the top of the chalk, after the deposition of the 

 Thanet Sands. 



1- — The flints never show any traces of having been rolled or worn by 

 the action of water, or broken up and weathered by any subaerial 

 agency, but are, except in colour, exactly similar to those in places 

 in the chalk. 



2. — No fossils, except chalk fossils preserved in flint, have been 

 found in it. 



3. — Where a nearly continuous bed of flints, or a large tabular mass of 

 flint occur, the base bed of the Thanet Sand seems to be arrested by 

 it in a manner that would suggest rather tlie chemical decomposition 

 than the mechanical erosion of the surrounding chalk, 



4. — Where masses of chalk are embedded in or surrounded by the base 

 of the Thanet Sand, this appears to be due to local undermining of 

 the main mass of the rock, and not to be transported fragments 

 re-arranged in a hollow. 



Again ; to look at the question from another point of view, it is highly 

 improbable that it could be otherwise. As water charged with 

 carbonic acid soaking through the Thanet Sand reaches the chalk 

 below, it must decompose the surface to a certain extent ; and if the 

 water can pass freely away so that new supplies, not saturated with 

 carbonate of lime, are brought to act upon it, that decomposition 

 must go on ad infinitum''' 



On the other hand, in the letter to the Geological Magazine of May 1866, 

 it was argued, 



" That as there is a great break between the secondary and tertiary 

 formations, it is natural to suppose that marine denudation had been 

 at work during the interval, removing the upper part of the chalk : 

 some such action might account for a bed of worn flints : but the 

 angular flints could not be accounted for by this means. The 

 occurrence of a semi-tabular broken flint points to upheaval and 

 fracture. And re-cemented flints which are here found, would 

 imply some slow action, during which the surfaces have been 

 re-combined. 



Should the chalk, immediately below the Thanet Sands, have been 

 subjected to subaerial action previous tothe deposition of the latter, 

 organic matter would be deposited along with the products of the 

 decomposition of the chalk, the green-coated flints being the result 

 of the combination of iron, silica, and alumina during this 

 process." 



The author likewise pointed out, that the tabular flints which 

 occurred between the chalk and the Thanet Sands, were, probably, 

 formed after the deposition of the latter, being the result of the 

 eilica of the sand brought in contact with the chalk." 



