AND LOAMS OF WEST HERTS. 1 oO 



Tlie beds usually consist of sands mixed with unworn flints, 

 subungular flints, and flint-pebbles. In some localities, as at Box 

 Lime, Wisi;gintou, and Markyiite Street, the bods of gravel and 

 sand are thin, while in othei's, as at Nomanshind and Couters End, 

 they are 12 feet or more in thickness. These gravels and 

 sands are probably of dilferent ages and were deposited under 

 various conditions. Those near Wigginton, at Box Lane, and in 

 some ]>arts of Berkhauisted Common, are associated in such a way 

 with the beds of loam occurring there as to indicate that they were 

 formed at the same time, as local variations of such beds. A few 

 deposits, like the one near Markyate Street, would appear to have 

 resulted from the subaurial denudation of areas which long remained 

 above sea-level in consequence of their being much higher than the 

 neighbouring sxibmerged districts. My survey of the higher parts 

 of the undulating country already described has led me to believe 

 that subaerial denudation has played not only an important but 

 a very great part in the formation of the superflcial deposits 

 covering such areas. The deposits occurring at JS^omansland and 

 near lledbourn may be old river- gravels. But whatever may have 

 been the agencies by which the flint-gravels and sands were formed, 

 the composition of these high-lying beds shows that most of their 

 component materials have not travelled far from their parent 

 deposits. 



Pebble-Gravel. 



The pebble-gravel, of which two undoubted beds are shown on 

 the map, is very different in mineral composition from the gravels 

 described above. It has been so named because it contains an 

 exceptionally large number of well-rounded pebbles of flint and 

 quartz. The larger pebbles are usually of flint and the smaller 

 ones of quartz, the number of small quartz-pebbles and grains 

 being so great as to give, in some cases, a greyish-white colour 

 to the matrix. There is a similar deposit near Bedmond, judging 

 from the presence of numerous quartz - pebbles there, but this 

 deposit has not been shown on the map. 



With regard to the age and mode of origin of the pebble-gravel, 

 Mr. Whitaker considers it to be the oldest drift-bed of this district, 

 and Professor McKenny Hughes regarded it as being, in all 

 probability, a marine deposit. The truth of both these views is 

 strongly supported by the evidence. 



Gravel and Sand (flint, quartzite). 



The gravels and sands, often associated with beds of loam, which 

 are shown on the map as occupying most of the low-lying part of 

 the undulating country previously described, are of considerable 

 economic value, since they furnish well- weathered and tougli road- 

 material, and an almost inexhaustible supply of sand and gravel for 

 building purposes. These deposits, classed as Middle Glacial bj' 

 Mr. S. V. Wood, and as " gravels of the lower plain " by Professor 



