﻿PRESTWICH ON THE DRIFT AT SANGATTE CLTFF. 



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washed appearance of all its component materials, 

 b In this it resembles any coarse, rough, shingle-beach, 

 jj I found, however, no traces of any shells in it. Above 

 ° this more regular bed is a roughly spread mass of 

 chalk-rubble and flint-gravel. The lower part, to a 

 thickness of 50 to 60 feet, consists essentially of a 

 paste of mixed sand, clay, and chalk, of a dirty cream 

 or greenish colour, and with imbedded fragments and 

 % masses of chalk, and here and there a large unrolled 

 « flint. Subordinate to this mass are irregular patches 



and layers of angular flint-gravel. The whole is 

 roughly bedded, or spread out, as it were, in irregular 

 sheets. The matrix of this chalk-breccia is liable to 

 frequent variations ; sands prevailing at one place, and 

 clays or chalk at another and on the same level*. 

 Occasionally the mass seems composed almost en- 

 tirely of greenish or of yellow sands, derived proba- 

 bly from the destruction of the lower Tertiary strata. 



Overlying this portion of the Drift, but still form- 

 ing part of the same deposit, is a mass consisting en- 

 6 tirely of angular flint- gravel, from 20 to 25 feet thick, 

 jp The matrix is the same generally as that of the por- 

 # tion below, from which it differs merely by the pre- 

 g ponderance of angular flints. It is composed princi- 

 ° pally of broken chalk-flints, but contains also a con- 

 siderable quantity of angular flat lumps of a coarse 

 iron-sandstone derived from a deposit of sand and 

 iron-sandstone, outliers of which overlie the chalk on 

 the adjacent hills. It also contains whole, as well as 

 sharply broken pieces of those peculiar green-coated 

 flints which form the lowest Tertiary bed in the north 

 of France and in England. Further, disseminated 

 irregularly throughout the mass, are a few of those 

 perfectly rolled and rounded black flint-pebbles, which 

 were formed at various periods during the Tertiary 

 epoch. These pebbles are sometimes whole, but at 

 other times they are broken, and their edges sharp 



1 and without wear. 



•g I met with no fossils in any part of this deposit. 



2 My visit to it, however, was very short. In structure 

 | and composition it so closely resembles the Brighton 



drift, and in some measure the drift at Dover, both of 

 which contain mammalian remains, — whilst in the 

 somewhat similar flint-gravel in the Department of 

 the Somme, and also in the gravel in the adjacent 

 part of the English Channel, such remains are not 

 uncommon, — that one of my objects in making this 



* Concreted masses, similar to the Combe-Rock of Dr. Man- 

 tell at Brighton, are not uncommon in the lower part of the 

 Drift. 



u 2 



