By Professor T. Rupert Jones, F.R.S., F.G.S., Sfc. 149 



has been stripped by denudation, is evident from the fact that in 

 many cases outliers of Plastic Clay [?] , and small portions preserved in 

 pot-holes, are scattered over the Chalk, and sometimes occur on the 

 very verge of the Chalk escarpment. It is most improbable, or 

 rather impossible, that under these circumstances the original edge 

 of the Eocene beds ran along the edge of the present escarpment ; 

 and the conclusion seems inevitable, that along with the Chalk the 

 Eocene beds have been denuded away from above the Oolitic strata 

 that lie on the north-west. The presence of many large and small 

 masses of the Greywethers on the surface of the Oolitic plains near 

 Swindon, and far beyond, would in this manner be easily accounted 

 for, and also the circumstance that below the Chalk escarpment they 

 are often apt to be less angular and more water-worn than the slab- 

 like blocks on the Downs, the reason being that they were probably 

 much more subjected to the influence of marine denudation during 

 oscillations of level, much of the Oolitic plains being below water 

 when the Chalk escarpment formed a late Tertiary line of coast-cliff/' 



§ 2. 



Memoirs Geol. Survey Gt. Britain, &c. Geology of parts of 

 Oxfordshire and Berkshire, Sheet 13. 1861. By E. Hull, W. Whita- 

 ker, and W. T. Aveline, pp. 47 and 48. " Greywethers .... 

 these remarkable blocks of hard light-coloured sandstone .... 

 occur in a similar manner to the north-west of Lambourne, a great 



part of which town is built of fragments of them 



Around Middle Farm, Knighton Bushes, Weathercock Hill, and 

 Hare Warren they are plentiful." From the measurements mentioned 

 above (page 124), Mr. Aveline observes "that the majority have a 

 thickness of about 2ft., as if they had come from one and the same 

 bed of sandstone. I have noticed similar correspondence in general 

 thickness in stones, many hundreds in number, covering the bottom 

 of one of the valleys to the west of Marlborough (in Sheet 34 of 

 the Geological Map) . Eastward of Lambourne there are often blocks 

 of sandstone on the Chalk, but no large collections of them, as in 

 the country to the west. They seem to occur in vast numbers only 

 where the Chalk is quite bare ; their number decreasing where that 



