Pleistocene Deposits at Ilford. 393 



above the gravel of the Cray and Darent Valleys, but below the 

 main gravel sheet which forms Dartford Heath (see bed h of Sect. 3). 



"This anomaly and seeming contradiction is due in my view 

 to the reversal of the drainage during the progress of the formation 

 of the Thames Valley, and the denudation of the Weald as discussed 

 by me in my paper in the Quart, Journ. Geol. Soc. 1871 (vol. xxvii. 

 p. 3)." 



In order to make the foregoing view more intelligible Mr. Wood 

 has most obligingly prepared a fresh Section (Sect. No. 3), and adds : 



'•' Crayford is nearer to the region of Wealden elevation than the 

 other localities of the Oijrena Brick-earth ; and this Brick-earth has 

 there been so elevated that the gravel of the Cray and Darent 

 Valleys (c of Sect. 3) forms in places a very distinct deposit occupy- 

 ing the valley bottoms, and lying at a level considerably below that 

 of the Cyrena Brick-earth. This gravel c is, in my view, a deposit 

 formed since the drainage was reversed into its present direction ; 

 the Cyrena Brick-earth, on the other hand, having been deposited 

 while the drainage from- the Thames Valley flowed into the sea 

 which covered the Weald. (See Section 3, p. 396.) 



" I should, however, point out, as one of the perplexing features 

 of this obscure subject, that if we follow the gravel c from the Cray 

 and Darent Valleys to the edge of the Stone marshes, and crossing 

 the Thames pursue it from its re-appearance above the West Thurrock 

 Marshes to the edge of the Cyrena Brick-earth at Grays, it seems 

 to inosculate with the gravel which (as shown in the section at 

 page 62 of the Third Volume of the Geological Magazine) parti- 

 ally underlies the Brick-earth at that place. I, however, believe 

 that this inosculation is not real, but that the gravel, c, really lies 

 up against the beds of gravel, sand, and Brick-earth which form 

 the Cyrena deposit of that place, and which are shown in the 

 present Section (No. 3) under the letter h. All the gravel and 

 Brick-earth beds occurring in the valleys of the Thames, and of 

 its tributaries, are now pretty generally admitted by geologists to 

 be posterior to the true Glacial period ; and their relation to the 

 extensive deposit of Glacial Clay which covers so much of the 

 Midland and Eastern Counties (bed No. 6) is shown by Section 

 No. 1 " (reprinted from page 43 of the Fifth Volume of this 

 Magazine) . 



To return to the Ilford Brick-fields, the Cyrena Brick-earth here 

 attains a thickness of nearly twenty feet. It may be seen in the 

 field on the London-road resting in one part direct on the London- 

 clay, while in another part it has a thin band of shingly gravel 

 beneath it. In the Uphall Brick-field its position relatively to the 

 newest gravel is best shown, the two deposits being unconformable 

 (see Section 2, reproduced here by permission of Mr. S. V. Wood, jun., 

 from Vol. III). 



When we consider the limited area from which the collection has 

 been made, it seems not a little remarkable that it should so well 

 represent the vertebrate fauna characteristic of these deposits, in 

 regard to the number of species ; whilst it greatly exceeds in number 



