154 T. E. LONES — GRAVELS, SANDS, CLAYS, 



represent the life of the period during which the beds were 

 deposited. This general absence of fossils greatly increases the 

 difficulties of correlating the beds. Thinlly, many of the materials 

 of the deposits, their sands, loams, flints, and well-rounded flint- 

 pebbles, closely resemble the corresponding rocks found in the 

 Cretaceous and Tertiary formations. The sands of the lowest 

 bed shown in the Aldenham sections are, for instance, scarcely 

 distinguishable from some of the sands of the Reading Beds at 

 Watford Heath and Harefield. The deposits are, in all probability, 

 to a large extent a result of the denudation of vast Chalk and 

 Tertiary beds which once existed over most of the County, but 

 have long since disappeared. Lastly, the various deposits of 

 gravel, sand, loam, and clay are distributed over the County in 

 a way so irregular and disconnected that, in ascertaining the 

 relative ages of the beds, the valuable test of superposition can 

 only be applied occasionally and partially. 



A. series of beds so variable, unfossiliferous, and apparently 

 disconnected cannot be satisfactorily correlated so as to allow a good 

 chronological classification to be made. Such a classification 

 would, for some purposes, be valuable, and would be welcomed 

 by geologists, but for practical purposes a classification based on 

 mineralogical composition is, perhaps, more useful. The following 

 table shows a classification of this kind, and gives the names of 

 a few places where the several beds are well exhibited : — 



The distribution of these beds is shown more clearly upon the 

 accompanying map, which is not intended to be a finished map, 

 but one from which such a map might be made. That part 

 which shows places lying south of the latitude of Berkhamsted and 

 St. Albans is similar, with the exception of a few alterations, to 

 the corresponding part of the excellent Drift map published by the 

 Geological Survey ; the rest of the map is new. A few of 

 the blank spaces on the map represent areas which I have not 

 surveyed sufficiently, but most of them show parts which ai-e 

 not covered by deposits treated of in this paper. 



