382 Reports and Proceedings — Geological Society of London. 



to the modes of occurrence of plumbago in other regions, and con- 

 trasts these with the surroundings of the Lake-District masses. 

 He points out that many thousand feet of volcanic rock supervened 

 between the Borrowdale plumbago-bearing rocks and the overlying 

 carbonaceous shales of Silurian age. On the other hand, he finds 

 similarities between the containing rocks in Borrowdale and the 

 diamond-bearing rocks of South Africa, and considers that the 

 conditions under which the plumbago was formed in the Lake 

 District approached much more closely to those which gave rise 

 to the Kimberley diamonds than to those which originated the 

 plumbago deposits in North America, though there is great dis- 

 similarity in the chemical composition of the intrusive rocks in 

 the two cases, especially with regard to the quantity of magnesia 

 present. He suggests that the molten magma in its upward 

 course passed through a deep-seated stratum of highty carbonaceous 

 material, and tore off numerous fragments, the bituminous matter 

 in which became acted upon by heat, a further alteration being 

 subsequently caused by the intrusion of the diorite. 



2. "Notes on the Valley-Gravels about Reading, with especial 

 reference to the Palasolithic Implements found therein." By 0. A. 

 Shrubsole, Esq., F.G.S. 



The following deposits containing implements are described : — 



A. North of the Thames. 



(i.) Gravel at Toot's Farm, Caversham ; 235 feet above sea-level, 



(ii.) Clayejr gravel by side of Henley Road, Caversham ; 168 feet 



above sea-level, 



(iii.) Subangular gravel at Shiplake ; 200 feet above sea-level. 



B. South of the Thames. 



(i.) Gravel at Elm Lodge Estate, Reading ; 197 feet above sea- 

 level, 



(ii.) Gravel on disturbed beds at Redlands ; 157 feet, 



(iii.) Comminuted flinty gravel at Southern Hill ; 223 feet, 



(iv.) Gravel at Sonning Hill ; 185 feet above sea-level, 



(v.) Gravel at Ruscombe, Twyford ; 165-170 feet above sea-level. 



The author concludes that the highest gravels (235-280 feet 

 above sea-level) do not, so far as is known, contain any traces 

 of Man, and that a considerable amount of valley-erosion occurred 

 before the deposition of the earliest gravels which have furnished 

 human relics. Further, he considers that the deposits indicate the 

 occurrence of a severe climate at an early stage, and its recurrence 

 at a later one, viz. during the deposition of the gravels found at a 

 height of 197 feet and 144 feet respectively above the sea-level. He 

 believes that many of the implements found in the lower levels at 

 Reading have been derived from gravels of various dates and different 

 levels, which have been swept away by denudation, and that this 

 will account for the mixed character of the types of implements. 



The next Meeting of the Society will be held on "Wednesday, 

 November 12th, 1890. 



