part 1] GAULT AlS^D LOWEK GKEEXSAND NEAE LEIGHTOIN'. 13 



Thickness in feet, 

 3. Oclireous conglomerate of partly-worn ironstone-fragments, grit-") 

 pebbles, etc. : in one place, capped by a ' table ' of hard iron-grit 

 46 inches long and 5 inches thick ; on a more or less continuous 

 floor of generally coarse iron-grit, but passing down in one place ^ 1 to If 

 into coarse green pebbly sand or grit. Iron-pans above the 

 floor, mostly broken up,>but with a few veins later than breccia- 

 tion. No limestone visible. Sharp base. 

 2. Silty beds : loamy greenish sands, clays, etc., as before; on tabular 



ferruginous concretions about 2 



1. Silver sand. 



That the bosses of h'on-grit formed crags on the sea-floor is 

 clear from all the ch'cumstances, and their presence is probably 

 responsible for the preservation of the smTOunding greensand, by 

 protecting it from the full sweep of the sea-cm'rents. The relation 

 of the ironstone of the crags to the underlying beds is not well 

 shown, either in my note-book section or in Mr. Schon's photo- 

 graphs, but may be explained by recent sections in pits on the 

 east, presently to be described. The masses were probably 

 indurated bosses of the main lower sands, with the breccia, etc. 

 banked around their undercut edges, as in the Nine Acre and 

 Miletree pits (figs. 8, 9, & 10, pp. 16, 18, & 19). 



The southerly working of the pit ceased not long after my visit 

 in 1906, for in March 1908 I found all the faces slipped and 

 obliterated, and the}^ have since been banked in by tip. 



I have entered fully into the particulars of my observations at 

 this spot, because it is held by Dr. Kitchin & Mr. Pringle that 

 the greensand beneath the Gault (which they never saw) must 

 have been ' Upper Grreensand ' brought into this position by Glacial 

 inversion, an idea irreconcilable with the facts. 



The structure of Shenley Hill in a north-and-south line, nearly 

 parallel to its axis, is shown in the reduced section (fig. 12, p. 22), 

 in which the sections observed in the contiguous pits are combined. 



The great variability of the beds immediately below the base of 

 the Gault in this region is exemplified to a still more striking 

 degree in a group of practically continuous sand- workings stretch- 

 ing eastwards from Shenley Hill, next to be described, as well as 

 by others on the north and west. 



The positions of the easterly workings are shown on the plan 

 (fig. 2, p. 5) ; most of them are still in operation, and the informa- 

 tion now to be given embodies the evidence which they presented in 

 the summer and autumn of last year (1920), supplemented in a few 

 cases by observations of earlier date. They have many features in 

 common, along with points of individual peculiarity ; the folloAving 

 descriptions and figures of the more important portions are arranged, 

 so far as possible, in an easterly sequence. Their relation to the 

 section at Harris's pit, above described, is showai in the combined 

 section (fig. 13, p. 22). 



