450 



MR. W. H. HUDLESTOK ON THE 



not expect the lithological contrasts to be strong or reliable in all 

 cases. The standard basal clays of the Middle Bagshots are nothing 

 more than a repetition on a higher horizon, and over a more extended 

 area, of argillaceous conditions which have obtained from time to 

 time throughout the so-called Lower Bagshots. 



The stratigraphical aspect of the question, as to the geological 

 position of the Hatch brick-earth, presents more material for our 

 consideration, though I am willing to admit that the evidence 

 presently to be adduced is not absolutely conclusive. Before 

 venturing on a diagrammatic section across country, let me recall 

 one or two facts in connexion with the Clay-pit. The lenticular 

 character of the deposit is obvious. The base may be taken at 

 60 ft. above O.D. where the mass is thickest, and this is about 

 25 ft. above the general level of the Thames at Chertsey. There 

 is a well commencing in the underlying sand, the mouth of which 

 is about 75 ft. above O.D. This well is said to be 35 ft. deep, all 

 in sand, and had 9 ft. of water in January 1887. This makes the 

 water-line in that part of Woburn Hill 14 ft. higher than the 

 general level of the Thames at Chertsey. Such indications point to 

 the probability of clay at no great depth from the bottom of the 

 well, since the well can hardly be deep enough to reach the valley- 

 water. At the same time I lay no very great stress upon this 

 conclusion ; first, because the various levels have not been ascer- 

 tained with absolute accuracy, and, secondly, because, in a Bagshot 

 country, the water is often held up so curiously and so capriciously 

 as to make us shy of draAving conclusions therefrom. 



Leaving the question of water-lines, let us consider how far the 

 general question of levels helps us to fix the position of the Hatch 

 brick-earth. With this object I now venture on a diagrammatic 

 section (fig. 3, p. 453). From St. Anne's Hill to the northern brow of 

 St. George's Hill is a distance of 5 miles, N.W.-S.E. St. Anne's Hill 

 is 230 ft. above O.D., and the north brow of St. George's Hill is 245 ft. 

 above O.D. Woburn Hill is just midway, with an elevation of 92 ft. 

 as a maximum. The position of the recognized basal beds of the 

 Middle Bagshots is very well known on St. George's Hill, and may 

 be placed at about 170 feet above O.D. The actual position of these 

 same beds at St. Anne's Hill is not quite so clear : but from general 

 considerations I am disposed to regard this hill *, in its normal and 

 unruined condition, as having the following composition : — 



* It is evident that opinions as regards this hill have varied at different times. 

 It owes its existence to an unusually thick deposit of Bagshot pebble-gravel, 

 which occurs quite at the top of the hill and presumably at the junction of the 

 Middle and Upper Bagshots. These pebbles are sometimes welded together as 

 a very hard conglomerate, and both this and the loose pebbles have been tumbled 

 about in every possible direction. St. George's Hill, on the other hand, is quite 

 different in shape, and owes its origin to a strong deposit of the older plateau- 

 gravel. 



It is admitted that the fixing of the line of the London Clay on St. Anne's 

 Hill is somewhat arbitrary, and seems rather opposed to the results of the 

 sinking for water at the Hollo way sanatorium (Whi taker, op. cit. p. 66). But 

 as we read of passage-beds (?) into the London Clay, there is evidently an eiemen 

 of uncertainty in the Report. 



