XX. 



THE GRAVELS, SANDS, CLAYS, AND LOAJIS OF WESTERN 



HERTFORDSHIRE. 



^A A 37 By T. E. LoNEs, M.A., LL.D., B.Sc. 



^ Head at Watford, 28th November, 1899. 



PLATE in. 



In that part of the County "which lies west of a line drawn 

 through Harpcndcn and St. Albans there are extensive gravelly, 

 sandy, and clayey deposits which rest upon the Cretaceous or the 

 Tertiary formation. These deposits may be theoretically separated 

 into two series, which merge into each other, and which were 

 deposited respectively before and after the time when certain 

 mammals, such as the musk- sheep, cave-hyjena, woolly rhinoceros, 

 and straight-tusked elephant, became extinct in this country. The 

 former series, with which alone this paper is intended to deal, 

 includes the Glacial Drifts and other beds formed at a time when 

 the physical geography and climatic conditions of the district were 

 very diiferent from what they are now. 



There is a close connection between the physical features of 

 a country and the nature and distribution of the deposits occurring 

 over its area, and for this reason a generalized account of the 

 physical features of Western Hertfordshire may serve a useful 

 purpose. In the north are many Chalk hills, which are in places 

 more than 600 feet above mean sea-level, and which form part 

 of the Chiltem Range ; these hills occur more especially in the 

 Tring, Aldbury, and Little Gaddesden districts. In the southern 

 part is a low-lying range formed by the Tertiary beds which end 

 off near Eickmansworth, Watford, and Shenley ; this range is 

 rarely more than 400 feet above mean sea-level, its average 

 height being about 300 feet. The part of the County between 

 the Chiltem Hills on the north and this low-lying range on the 

 south is gently undulating, and is intersected by comparatively 

 wide and shallow valleys in whicli flow the Ptiver Colne and its 

 tributaries the Ver, Gade, and Chess. It is over this undulating 

 tract of country, with its charming combination of hill and vale, 

 woodland and meadoAv, that the gravels, sands, clays, and loams 

 described in this paper almost entirely occur. 



These beds present several important characteristics. Firstly, 

 they are exceedingly variable, a section at one place being 

 usually very diiferent from another at no great distance. Sections 

 1 and 2 (p. 155), taken in a gravel-pit on the west side of 

 Aldenham, show how rapidly some of the beds thin out and arc 

 replaced by others which thin out in turn. The distance between 

 the sections was less than 9 feet. Secondly, as a general rule, 

 • the beds are unfossiliferous in the proper sense of the word ; fossils 

 occur in some of the deposits, but they are derived and do not 



VOL. X. — I'ART V. 12 



