124 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



ganisms tt) assist in the determination, generally referred to the age 

 of those sands*. The weight of evidence is however, I think, against 

 the origin usually assigned to them, although that evidence is cir- 

 cumstantial rather than direct. 



In the first place, if they were derived from the Bagshot Sands, 

 it is difficult to conceive why they should not he scattered as com- 

 monly over the generally broad belt of London clay intervening be- 

 tween the area of the Bagshot Sands and the Chalk, as they are 

 over the area of the latter ; — that connecting links should not have 

 been left between the parent beds and the groups of greyweathers 

 scattered over Marlborough Downs and the Chiltern Hills. But no 

 such general pheenomenon is exhibited within the London-clay area. 

 It is further to be observed, that the Bagshot Sands (the lower divi- 

 sion) themselves, although well developed between Strathfieldsaye 

 and Newbury, do not in that district contain any large blocks of 

 sandstone f . In Kent, over no part of which county do the Bag- 

 shot Sands extend, the Druid sandstone is abundant on many parts 

 of the chalk hills. No fringe, in fact, of detached sandstone blocks 

 skirts the Bagshot Sands, whereas wherever such scattered groups 

 do occur they invariably subtend either the main body or detached 

 outliers of the Lower Tertiaries. 



On some of the high hills towards the borders of the extensive 

 chalk downs forming Salisbury Plains, especially to the northward 

 and eastward of Amesbury, or between that town, Bedwin, and 

 Kingsclere, cappings of the lower tertiary sands and clays are not 

 uncommon ; whilst other hills, where no mass of tertiaries remain, 

 show by the presence of numerous tertiary flint-pebbles on their 

 summit the wreck of tertiary strata once spread over this area. The 

 drift of the district also often abounds with these characteristic 

 pebbles. At Marlborough the tertiary strata range up close to where 

 the dispersed blocks of sandstone commence. A ridge of hills 

 formed of these lower tertiaries on a base of chalk dominates over 

 the platform of the latter formation for some miles in a direction 

 W.N.W. from Newbury. As it trends westward the bed of sand 

 immediately over the chalk expands, becomes extremely Avhite and 

 pure, and in one place, just below Wickham Church, contains at 

 its base a few seams of pebbles and worn subangular flints. It is 

 precisely the unconsolidated substance of the Druid sandstone ; still 

 I could not find, nor had the foreman who had worked twenty-one 

 years in some adjoining pits ever found, a block of sandstone hi situ 

 in the sands. But then it must be considered how small an extent 

 of this bed is opened out, — only two or three regularly worked pits 

 in the distance of six miles, — and the extremely small proportion 



* Not, liowever, universally so : by some geologists the origin of these blocks 

 has been correctly rcfen-ed to the " Plastic Clay Formation," but no proofs have 

 yet been oft'ered in support of the suggestion. 



t So rare is it, in fact, to find any blocks of stone in that part of the country, 

 that a small mass of about a foot square, lying on the gravel of Silchester Com- 

 mon, has been considered of sufficient importance to have a local name assigned 

 to it — " The Nymph Stone." 



