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MESSES. H. W. MONCKTON AND R. S. HEEHIES 



plan presented by the beds on the overlap theory. It cannot be 

 denied that the Middle Bagshot beds make their appearance at the 

 surface all round the central mass of the Upper Bagshots ; and 

 then around this, according to the proposed reading, is an outlying 

 ring of Upper Bagshots, a kind of Saturn's Eing to the central planet, 

 as represented by the Eox Hills, Chobham Hidges, and Easthamp- 

 stead Plain. This may seem to be putting the case rather too 

 strongly ; but we think that whatever it is, Upper, Middle, or Lower, 

 this outer ring mapped by the Survey as Lower and in part claimed 

 by Mr. Irving as Middle and Upper, must all go together, at least 

 along the north and south of the main mass. Such a feature as 

 would thus be presented must be admitted to be most unusual. Then, 

 again, the overlap theory requires the London Clay to have as- 

 sumed a basin-shape before the deposition of the Bagshot series 

 upon it ; and this would require a considerable interval of time, so 

 much perhaps as to give support (were it not for fossil evidence) to 

 the old theory alluded to by Professor Prestwich (Quart. Journ. 

 Geol. Soc. vol. iii. p. 380), that the beds in question correspond in 

 age with the Crag of the Eastern Counties. 



But the authors, though they think that the evidence, such as it 

 is, goes to show that the Lower Bagshot does not rest conformably 

 on the London Clay, yet consider that there is a general uniformity 

 in the lie of the beds, — that the interval in time between the 

 deposition of the London Clay and the Lower Bagshot was not, by 

 comparison, considerable, — and that the same earth-movements 

 which gave a basin-shape to the London Clay had a precisely 

 similar effect on the overlying Bagshot Series. 



Stress has been laid on the fact that no pebble-beds have been 

 recorded in the Lower Bagshots in well-sections ; but unless their 

 insignificance has caused them to be overlooked, their absence is but 

 a further proof of the irregularity of their occurrence. 



With regard to the relative thickness of the beds at various points, 

 we can only say that measurements obtained from well-sections alone 

 should not be accepted too readily, and we can hardly expect to find 

 that the beds would retain the same thickness throughout an area 

 so large as that under discussion. 



We think we have now said enough to fulfil the objects of this paper 

 viz. : — to give additional details of the Lower Bagshot beds of the 

 area of Bagshot Heath, and to defend, we hope successfully, the 

 interpretation of the succession of beds in this district, originally 

 suggested by Professor Prestwich, and adopted and confirmed by 

 the Geological Survey, from the vigorous attack recently made on it. 



And, in conclusion, we claim to have proved that the Lower 

 Bagshot is not overlapped by the Upper and Middle portions of the 

 series, and that the Bagshot strata do, as a whole, lie in a synclinal 

 curve. 



