454 



MR. W. H. HUDLESTON ON THE 



Hence at Chertsey the London-Clay surface almost coincides with 

 the Ordnance Datum. At the junction of the Wey and Thames I 

 have no record, but the well-sinker at Oatlands (Mr. Gray) considers 

 that the " blue clay " will not be quite so low there as at Chertsey. 

 At West Molesey the London-Clay surface is 7 ft., and at Thames 

 Ditton, 14 ft. above O.D. If these places in the valley of the 

 Thames itself fail to afford a London-Clay surface below O.D., how 

 much less likely is it that the flanks of that valley should do so ? 

 Unless there are exceptional circumstances, of which we have no 

 proof, I should be disposed to run the line of junction between the 

 London Clay and the Bagshot beds in "Woburn Hill at from 20 to 30 

 ft. above O.D. The effect of this would be to bring the Hatch brick- 

 earth comparatively low down in the Lower Bagshots, and pretty 

 nearly on the horizon of the clays distinguished as ~No. 4 of the 

 Walton- Oatlands cutting. 'Not that these two deposits are by any 

 means to be regarded as continuous, since ail the evidence goes to 

 show that clays occur in an irregular and sporadic fashion through- 

 out the sandy beds of the Lower Bagshots. 



7. Conclusion. 



It may be asked why so much importance should be assigned to 

 the position of these Bagshot clays, or, to put it more plainly, why 

 a particular brick-earth should be relegated to the Lower rather 

 than to the Middle Bagshots. 



There are two principal answers to this question. First, that we 

 should not neglect any opportunity of studying the Lower Bagshots of 

 the London Basin, with a view to ascertaining their composition 

 and development throughout the district. The term " Lower Bag- 

 shot Sands," applied by some people, is thoroughly misleading, as 

 lithological terms usually are in such cases. But altogether apart 

 from the question of nomenclature, there arises a desire to possess a 

 more complete knowledge of these curious beds. The more they are 

 studied under favourable opportunities and without prejudice, the 

 less we shall hear of a passage between a uniform deposit with 

 marine organisms, like the London Clay, and the irregular, current- 

 bedded sands, loams, and clays which constitute the beds usually 

 known as the Lower Bagshots. At present we really know very 

 little of the junctions between the London Clay and the Bagshot 

 Beds ; since those of well-sections are not very satisfactory, 

 owing to the different appearance which the same beds are apt to 

 present under a different state of oxidation, and ' also, in some 

 cases, to the unfitness of those who have to prepare the sectional 

 reports. 



The second answer to the inquiry, as to the utility of these 

 investigations, is mainly derived from the following consideration, 

 viz. : that, until observers fairly realize the existence of important 

 masses of clay and loam in the division usually known as the Lower 

 Bagshots, we shall be continually finding beds referred to the 

 Middle Bagshots which stratigraphically do not belong to them. 



