PRESTWICH — WOOLWICH AND READING SERIES. 



153 



For a small section of the Basement-bed and of the upper part 

 of the Woolwich series at Stratford see Journ. Geol. Soc. vol. vi, 

 p. 262. 



The sections of wells which I have from Ilford, Romford, Brent- 

 wood, and adjacent districts give us no particulars of the Lower Ter- 

 tiaries, as water was in all cases obtained almost directly after passing 

 through the London clay. Some preliminary works for an artesian 

 well by the Local Board of Health at Chelmsford have, however. 



mottled character and passing into a brown micaceous sandy clay. An instance 

 of this has recently come before me in the section of a trial boring made opposite 

 Blackwall. Beneath 33 ft. of peat and gravel were 55 ft. of brown clay, which had 

 been mistaken for the London clay. At first sight it certainly a good deal resembled 

 it, but on a closer examination it presented characters decidedly differing from that 

 clay, which is of a hghter brown, or else bluish, more homogeneous, and is not 

 so micaceous. It is in all cases very necessary to guard against well-sections 

 not recorded with sufficient care. Several of those collected by Dr. Mitchell are 

 in all probability given wrong by the well-digger, as one near Waterloo Bridge 

 (W.), which brings the London clay too near to the chalk. 



W. Feet. 



Gravel and sand 40 



Blue clay 110 



Red clay 10 



Sand 5 



To the Chalk 165 



Whilst in another well at Finsbury the 

 mottled clays are omitted altogether. 

 Feet. 



Gravel and London clay 160 



Sand and pebbles 10 



To the Chalk 170 



The same fact is observable in some of the sections collected by the Commis- 

 sioners of Sewers ; as for instance — 



Well-section, Coding's Brewery. 

 Feet. 



Made ground 15 



Gravel 15 



Blue clay 160 



To the Chalk 190 



Well-section, Thome's Brewery. 

 Feet. 



Made ground and gravel 40 



Blue clay 162 



To the Chalk 202 



(See p. 148.) 



Well-section near Westminster Bridge. Mortlake. Barnes. 



Feet. Feet, Feet. 



Made ground and grave! 27 10 18 



Blue clay 160 180 180 



To the Chalk 187 190 198 



Some mistake is evidently made in these sections in carrying the London clay 

 down to the chalk. In some others too great an extension has apparently been 

 given to the beds of flint pebbles (called gravel), as they appear to occupy the 

 place of the Thanet Sands as well as their own : — 



Well-section, Bermondsey. 



Feet. 



Bog earth and peat 9 



Silt 3 



Quick sand 20 



Blue clay 60 



Gravel 110 



202 



Well-section, Seager's, Milbank. 



Feet. 



Made ground 22 i 



Gravel 3 



Blue clay 93 



Blue rock 2 



Sand and gravel 77^ 



To the Chalk 198 



