SUEFACE-DEPOSITS OF THE EALIlfG DISTRICT. 195 



summit of Castlebar Hill ; vegetable remains have been found in it. 

 This brick-earth therefore forms a bed in the gravels more than a 

 quarter of a mile long. 



The partial absence of the valley-deposits from this London-Clay 

 area is doubtless due to denudation ; and this may probably have 

 been brought about by the same conditions which laid bare the 

 strips of London Clay which, as Mr. Whitaker has observed, separate 

 the high-terrace from the mid-terrace deposits. 



I have found that beds of loam and gravel, apparently corre- 

 sponding in age and level with the high-terrace gravel (between 90 

 and 130 feet), may be traced in the country to the north of the 

 ridge which, in this district, has usually been considered to be the 

 limit of these deposits. The evidence is briefly as follows : — A bed 

 of mottled sandy clay was lately exposed on the north side of the 

 avenue leading to the grounds of Twyford Abbey. It was about 5 

 feet in thickness, and traceable fully three quarters of a mile along 

 the road eastward (about 117 feet above O.D.); it extended* some dis- 

 tance up the northern slope of the hill forming part of the ridge. I 

 have seen sections of gravel 7 or 8 feet thick at Alperton, and noticed 

 at the base of the deposits a bed of large-stone gravel (like that 

 which characterizes the base of the high-bench gravels), containing 

 blocks of abraded Sarsen stone, one of which was 3 feet across 

 and must have weighed about 7 cwt. 



Beds of about 8 feet in thickness occur in brick-fields at Sudbury, 

 while a low hill to the east of these works is largely composed of 

 vaUey-deposits which are said to be of the depth of 25 feet. I saw 

 many boulders of water-worn Sarsen stone which were taken from 

 it, from 18 inches to more than two feet in diameter. Eastward of 

 Acton Wells there is a considerable deposit of sand at 106 feet above 

 0. D. At Harlesden Green (about 140 feet above 0. D.) and its 

 neighbourhood, brick-earth occurs in patches, while valuable beds of 

 the same material likewise occur at Harrow Weald, Northolt, and 

 Greenford ; large boulders of Sarsen stone are found on or just be- 

 neath the surface of the land. 



These facts appear to indicate that during the period when the 

 lowermost beds of the high bench were being accumulated, similar 

 gravels of less thickness were being laid down on the Eocene area to 

 the north, and that such formations may have continued up to the 

 time when the brick-earth series set in. 



Old Land- Surfaces. — The high-terrace gravels between 60 and 125 

 feet contain seams of black matter (carbonate of iron or manganese). 

 These appear to be due to the decay and consequent change of vege- 

 table matter : on examining them I found that their position and 

 relation to each other were more or less persistent in the neighbour- 

 hood of Ealing. I soon noticed that a very distinct stratum was 

 almost always apparent close beneath the brick-earth deposits, and 

 that when the floor was not indicated by a seam of black matter, it 

 was to be traced by beds of whitened pebbles and subangular frag- 

 ments. Many of these fragments are coated with a deposit which 

 looks like clay ; but as it does not break up in water, it may be a 

 clayey humus. The stones, moreover, are often eroded in such a 

 Q.J.G.S. No. 166. p 



