. Sir H. a. Soicorth — The Mammoth and the Glacial Drift. 401- 



The Boulder-clay caps the ridges of Navesden and Hammer Hill, 

 bounding the valley on either side ; but within the valley itself, 

 including the elevation of Summerhouse Hill, there is no glacial 

 deposit. That Hill divides the valley into two troughs, in each of 

 which the drift gravels with Mammalian bones and shells are found, 

 and in each these gravels repose on the Oxford Clay and that on the 

 Limestone of the Middle Oolite. 



I am further bound to say that in Mr. Wyatt's section, published 

 in the Geologist for 1861, page 243, and again by Mr. Prestwich 

 in the Q.J.G.S. vol. xvii. p. 364, the Mammal and Implement bed 

 at Biddenham appears to be overlain by drift. 



Turning from Bedfordshire the only discovery of interest in 

 Central England in the present discussion was made in Hertfordshire. 



Professor Prestwich, writing in 1858, says: "A ballast pit has 

 recently been opened at the Watford end of the Bricket Wood 

 cutting, and immediately south of the line, which exposes a section 

 of much interest. The Boulder-clay has there almost thinned out, 

 leaving but a seam one or two feet thick, whilst above and below it 

 is a thick bed of gravel. . . • The lower gravel I believe to pass 

 under the Bonlder-clay. ... In the ballast pit I was fortunate 

 enough to discover in tlie lower gravel a few pieces of the tooth 

 and tusk of the Elephant, . . . The lower gravel reposes upon an 

 irregular surface of chalk (Geologist, 1858, p. 242). 



Let us now turn to the Welsh caves. 



Dr. Buckland says that in 1836 he found, on the property of 

 Mr. Lloyd near Cefn Cave, fragments of marine shells associated 

 with the usual detritus, and inferred from the fact of Mr. Trimmer 

 and Dr. Scouler having discovered recent marine shells and drifted 

 pebbles over the bones in the cave, and from the admixture of the 

 bones of mammifers with diluvium in Kirkdale, Torquay, and other 

 caverns, either that these caves were submerged subsequently to 

 their having been inhabited and again raised above the level of the 

 sea, or that vast irruptions of water, apparently loaded with icebergs, 

 had overwhelmed the country (Proc. Geol. Soc. vol iii. p. 584). 



Making allowance for the geological language which then pre- 

 vailed, this means that so far back as 1836 Dr. Buckland had affirmed 

 that the Mammalian bed in the Cefn Cave was overlain by drift. 



Mr, D. Mackintosh, in speaking of the Cefn and Pont Newydd 

 Caves, refers to the clay in the cavern as containing angular and 

 subaugular fragments of limestone, a few polished fragments and 

 pebbles of limestone, and a few pebbles of Denbighshire sandstone 

 and grit, felstone, etc., and he says: "It is horizontally continuous 

 with the Upper Boulder-clay of the district. The clay, he says, 

 can be traced along the plain of Lancashire and Cheshire, the 

 coast of Flintshire, and up the Vale of Clwyd. It spreads over 

 the gently rising ground between St. Asaph and the Cefn and Pont 

 Newydd Caves, and it may be seen all round the caves, in some 

 places filling up hollows, in others covering plateaux, and in not 

 a few instances clinging to the face of steep slopes, or even ad- 

 hering to narrow rock terraces or ledges. I have been familiar 



DECADE III. — VOL. IX. NO. IX. 26 



