ON A RECENT SUBSIDENCE AT MUCKING, ESSEX. 245 



about 100ft., though the depth to the Chalk varies from 8ft. to 

 150ft. 



At the Mucking Hole we have not merely the full thickness 

 of the Thanet Sand, but also that of the Woolwich and the 

 Blackheath beds between the surface and the top of the Chalk. 

 For the strata seen in the sides of the pit evidently belong to 

 the basement bed of the London Clay. And the Geological 

 Survey map shows London clay around the spot where the pit 

 exists, while it evidently would also be found where the older 

 depressions appear in the field westward, beneath the gravel 

 forming the surface. 



As regsrds the " Basement-bed " of the London Clay, the 

 following details may be useful. Mr. W. Whitaker remarks in 

 his Memoir, The Geology of London and of Part of the Thames 

 Valley, Vol. I., p. 238 : — " Immediately at its base the London 

 Clay commonly contains a greater or lesser admixture of green 

 and yellow sands, generally mixed with rounded flint pebbles, 

 and not unfrequently cemented by carbonate of lime into 

 semi-concretionary tabular masses. These mixed beds, how- 

 ever, never exceed a few feet in thickness, and pass upwards 

 rapidly into the great mass of the London Clay. To this part of 

 the formation Mr. Prestwich has given the name of the ' base- 

 ment bed.' " 



The nearest section that I can find which will illustrate the 



nature and thickness of the strata between this basement bed of 



the London Clay and the top of the Chalk in this district is that 



of the well at Broad Hope Farm, about a mile eastward of 



Stanford-le-Hope. It is given in Mr. Whitaker's collection of 



Essex Well Sections (Part IV.) Essex Naturalist, Vol. IX,, 



p 178. For our present purpose a somewhat condensed account 



of it will suffice : — 



ft. in. ft. in. 



London Clav ■< 1 ' " J * " * j * 



- (clay and sand 5 



Blackheath Beds (sands and gravels) 49 8 \ 



Woolwich Beds (sand, gravel, and a little clay) 33 6 \ 147 2 



Thanet Sand (sand) 64 ) 



Chalk 



The section at Thames Haven, given in Mr. Whitaker's memoir, Geol, 



Land., etc., Vol, II. p. 37, shows, when similarly treated : — 



London clay ft. in. ft. in. 



Oldhaven (or Blackheath) Beds (sand) 5 3 \ 



Woolwich and Reading Beds (sand and sandy clay) 33 3 > 150 



Thanet Beds (sand and clayey sand) ill 6 J 



Chalk 



