Note on the Junction of the Thanet Sand and the Chalk, and of the Sandgate Beds and Kentish Rag

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Abstract
At the bottom of the Thanet Sand there is always a bed of greencoated flints in a green and rust-brown clayey sand. 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 Sand:— 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 subaërial agency, but are, except in colour, exactly similar to those in place 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 occurs, the base-bed of the Thanet Sand seems to be arrested by it in a manner that would suggest rather the chemical decomposition than the mechanical erosion of the surrounding chalk. 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 The only difference, therefore, between this action extending over the whole surface of the chalk where covered by Tertiary or later deposits and

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