450 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 19, 



the whole of the high-level gravel of Mr. Prestwich may be nothing 

 more than higher terraces of the valley-graveL 



To enable the reader to understand at a glance the positions of 

 the gravels I am about to describe, I have drawn a map of this part 

 of the Thames valley, with contour lines of 10-feet levels strongly 

 marked. A portion only of this map is given in the accompanying 

 illustration (fig. 1), showing the part of the valley between Acton and 

 the Thames. The margin of the London Clay is here shown by a 

 dark tint, that of the gravel by a light one, and, for the sake of 

 clearness, no distinction is made between the gravel and brick-earth. 

 The geology of this district is taken chiefly from Mr. Mylne's map*, 

 the accuracy of which I had the means of verifying in several places. 

 The heights in this and all other cases are taken from the Ordnance 

 datum, viz. mean tide at Liverpool, which is 12| feet lower than the 

 Trinity datum of Mr. Mylne's map. 



The valley-gravels proper of this neighbourhood, which for our 

 present purpose may be roughly, though not accurately, described as 

 the gravels lying below the 100-feet level, have been divided by 

 Mr. Whitaker into three terraces, which it may be advisable here to 

 describe, viz. : — a high-terrace gravel, occupying the shoulders and 

 sides of the valley at a height of from 50 to 90 and 100 feet above 

 the datum ; a mid terrace, from 20 to 30 feet high, in the bottom of 

 the valley ; and a low terrace, occupying the low ground in the salient 

 bends of the river, at an average height of from 1 to 20 feet. 



Commencing with the north side of the river, he traces the margin 

 of the uppermost river-terrace, or high terrace, as it may be conve- 

 nient to call it, in contradistinction to the high-level gravel of Mr. 

 Prestwich — from Drum Lane, north of Brentford, passing a little 

 below Gunnersbury to Acton and East Acton, where this terrace 

 ends off ; and the next, or mid terrace, runs up at Wormwood Scrubs 

 as far as the London Clay. 



The northern boundary of the high-terrace gravel extends to be- 

 yond Hanwell on the west, passing by Ealing to Acton, where it is 

 cut by a strip of the London Clay in the ravine of the Acton brook, 

 dividing it from the isolated patch of high-terrace gravel to the 

 eastward, which forms the particular subject of this paper. The 

 average height of the northern limit of the high terrace is about 

 100 feet. 



From Kensington to the Serpentine the high terrace is again 

 found, rising at Campden Hill to the height of 129 feet, and extending 

 beyond the Bayswater Road to the northward. Eastward of the 

 Serpentine it rises again, extending from Piccadilly to Regent's Park, 

 and from Paddington on the west to Einsbury on the east. 



AU the country to the north of this terrace, with the exception of 

 a patch of gravel in the vaUey of the Brent, north of Twyford, and 

 some other patches beyond the limits of the tract under consideration, 

 consists of the London Clay ; and strij^s of the London Clay also run 

 round the patches of high-terrace gravel along the sides of the 

 Thames valley, at an average height of 50 feet, dividing it from the 



* Greological Map of the Contours of London and its Environs. By E. W. 

 Mylne, C.E. 



