404 Rev. Dr. Irving — Elevation of the Weald. 



answers. In my first paper 1 on Tertiary Geology, read before the 

 Geologists' Association in 1883, I pointed out that the presence of 

 Eocene pebble-beds in the Woolwich and Beading series and in the 

 Bagshot series afforded strong evidence of the encroachment of the 

 sea upon the Upper Chalk in Eocene times. This conclusion is 

 accepted by our greatest authority on Tertiary Geology, Prof. 

 Prestwich. 2 The fact alone furnishes a strong presumption that 

 the elevation of the Weald had commenced before the close of the 

 Eocene period ; while the many outliers of the Woolwich and 

 Beading beds at high altitudes on the N. Downs, taken along with 

 the general absence of the London Clay there, seems to tell us that 

 the initial elevation of the Weald hill-range had gone far enough 

 for this to form a shore to the area of deposition of the London 

 Clay. I have shown furthei', in a former volume of the Geol. 

 Mag., 3 that, though there is no absolute proof, there are grounds 

 for believing, that certain outliers of sands on the N. Downs (at 

 Chipstead, Headley, and north of Netley Heath) are more likely to 

 turn out to be of Upper Eocene age, than of any age to which they 

 had been hitherto assigned by different writers. There is here the 

 strong presumptive evidence of the lithological similarity to the 

 Upper Bagshot, in most cases amounting almost to identity. In 

 the Headley sections, as I saw them, there was just that difference 

 in the beds being thinner than is usual in the Upper Bagshot, and at 

 the same time the presence of a few scattered small unworn flints in 

 the sands, which made me speak of them with more reserve ; but 

 which further consideration has suggested may be only just those 

 differentia which may be explained by greater proximity to a shore, 

 where the Chalk was undergoing destruction and furnishing the 

 flints. On the other hand, there was on the surface what appeared 

 to be the wreckage of a Bagshot pebble-bed at Headley, which 

 suggests the Lower Bagshot as the more probable horizon for the 

 sands at that place. Still these facts taken together do not of course 

 militate against the view that the sands at the various localities 

 mentioned may be of Upper Eocene (Bagshot) age. 



To the minds of some the question as to age of these beds may 

 appear to have been definitely settled, now that the Lenham deposits 

 are shown to be of Diestian age, i.e. Older Pliocene. 4 This, of 

 course, depends upon the contemporaneity of these deposits with the 

 Lenham beds (some fifty miles further to the east) being estab- 

 lished. This contemporaneity has been generally assumed on the 

 ground of approximate equality of altitude above the sea ; but this, 

 after all, may be a mere accident, and if so any argument based on 

 the assumption must give way ; the chain cannot be stronger than 

 than its weakest link. This assumption seems to be based on the 

 further assumption that the elevation of the Weald has been 



1 On the Bagshot Beds of the London Basin and their associated Gravels, Proc. 

 Geol. Assoc, vol. viii. pp. 143-171. 



2 Q.J.G.S. vol. xlvi. pp. 116, 167. 



3 See Geol. Mag. Dec. III. Vol. V. (1888), pp. 183, 184. 



i See Mr. Clement Beid's communication to Nature (1886), vol. xxxiv. pp. 341-2. 



