G-EOLOGICAtj NOTES. 



as shown in a gravel pit, from 8 to lo feet deep and from 30 to 

 40 yards broad, in the beds lying above the London Clay at the 

 top of the hill. The gravel is largely subangular, and resembles 

 in its general character that of the marshes below. And the 

 loamy material by which it is more or less covered is evidently 



Fig. I. Higham Hill Gravel, &c. Height of Section 6ft; length 20ft. 



the equivalent of that which forms the surface bed in the reser- 

 voir excavations. (Fig. i). But the Higham Hill deposits are 

 shown only in an ordinary gravel pit. While the gravel, loam, 

 &c., in the area occupied by the reservoirs, have been displayed 

 in sections hundreds of yards in length and ranging in every 

 direction. Consequently the latter gave not only exceptionally 

 good opportunities for noting variations in details, but their 

 length, and the changes in their direction, combined to throw 

 much light on the local changes of conditions to which the varia- 

 tions in the nature and thicknesses of the beds were due. An 

 additional advantage which they possessed, of an exceptional 

 kind, lay in their cutting across a deserted channel of the Lea. 

 Then, while the largest gravel pits or brickyards usually show 



Fig. la. Hii^ham Hill Gravel, &c. Height of Section, 8ft., length, 30ft. 



clear sections over but a fraction of their total expanse, the 

 reservoir excavations were almost everywhere fresh and distinct, 

 and they were free from the sloping which is so • geologically 

 pernicious in the case of new railway cuttings. 



The depth from the surface of the sections in the reservoir 

 excavations varied from about 9 to 11 feet. They always showed 

 loam or clayey loam at the surface and gravel at tlie bottom, 

 though the thicknesses of the two beds varied considerably. In 

 one place, for perhaps 150 to 200 yards or more, gravel, capped 

 by from ift. 6in. to 2ft. of loam and soil, constituted the whole 



