346 



Mr. G. Jennings Hinde. 



[May 21, 



II. "On Beds of Sponge-remains in the Lower and Upper 

 Greensand of the South of England." By George 

 Jennings Hinde, Ph.D., F.G.S. Communicated by Henry 

 Woodward, LL.D., F.R.S. Received April 29, 1885. Read 

 May 21. 



(Abstract.) 



I have pointed out in this paper the occurrence in the Lower and 

 Upper Greensand strata of the Wealden area, the Isle of Wight and 

 the south-western counties, of beds of rock formed to a large extent 

 of the detached spicular remains of siliceous sponges, and thus 

 distinctly of organic origin. Their true characters have not been 

 generally recognised, and they have usually been described as deposits 

 of sandstone, chert, malm, hearthstone, firestone, &c. In the Lower 

 Greensand these beds are mainly developed in the lower, or Hythe, 

 division, and they are exposed at Haslemere, Midhurst, Petworth, 

 Godalming, Tilburstow Hill near Godstone, Sevenoaks, Maidstone, 

 and at Hythe. The sponge-beds vary from three-quarters of an inch 

 to three feet in thickness ; between them, as a rule, there are inter- 

 vening beds of sand or sandstone. The greatest total thickness of the 

 sponge-beds exposed in any one section is 11 feet. Sponge-beds are less 

 common in the higher or Folkestone division of the Lower Greensand, 

 but they are numerous at Folkestone itself, and reach a total thickness 

 of more than 8 feet, and there is also a thin bed in this division at 

 Sevenoaks. The Lower Greensand strata at Faringdon, in Berkshire, 

 are of an altogether different character to those of the same formation 

 in the area treated of in this paper, and the sponges which abound 

 therein are likewise entirely different, being calci sponges, and 

 retaining their entire forms. 



The sponge-beds in the Upper Greensand are of two distinct types, 

 one of which is shown on the northern and western margin of the 

 Weald, and the other in the Isle of Wight, and further westward in 

 the counties of Wilts, Somerset, Dorset, and Devon. In the first- 

 named district the sponge-beds are of a soft, greyish-white, siliceous, 

 or siliceo-calcareous rock, known under the names of malm, hearth, or 

 firestone. In this the sponge spicules principally occur in the 

 negative form of minute empty casts, the presence of which renders 

 the rock extremely light and porous. The beds can be traced nearly 

 continuously along the northern and western margin of the Wealden 

 area, and they are well shown at Godstone, Merstham, near Reigate, 

 Betchworth, Farnham, and Selborne. Further northwards they are 

 present at Wallingford, in Berkshire. The beds vary in thickness 

 from 15 feet at Merstham to 60 feet at Farnham. 



In the more typical Upper Greensand of the Isle of Wight and the 



