156 Proceedings of Philosophical Societies. [Aug. 



are all abandoned. They consist of galena mixed with pyrites, 

 and with the carbonates of lead and of copper. They lie in 

 grey-wacke ; but at Foxdale they have been followed into the 

 subjacent granite. The mean temperature of the island is 

 49-99°. 



On the 1 8th of June a large specimen of nodular agate was 

 exhibited to the Society by Dr. Curry, which he conceived to 

 point out a natural connection between agate and the plasma of 

 the ancients. 



Part of a paper, by Mr. Webster, was read, on the fresh 

 water formations of the Isle of Wight, with some observations 

 on the strata lying above the chalk in the south of England. 

 The observations in this paper were partly suggested by the 

 memoir of Cuvier and Brogniart on the strata in the neighbour- 

 hood of Paris. Sir Henry Englefield first observed the highly 

 inclined strata of chalk in the Isle of Wight. He entrusted the 

 accurate survey of these curious strata to Mr. Webster. The 

 present paper is the result of his examination. . 



An elevated ridge of hills runs through the Isle of Wight, in 

 a direction nearly E. and W. from Culver Cliff to the Needles. 

 These hills are composed of strata sometimes nearly vertical, but 

 generally forming an angle with the horizon of from 60° to 80°, 

 dipping northward. The strata consist of the uppet and lower 

 beds of chalk ; that is, of the chalk with and without flints, 

 covering the chalk marl ; and these again are underlayed by 

 calcareous sand-stone, with subordinate beds of chert and lime- 

 stone, clay and carbonized wood. To the north of these strata 

 occur, at Alum Bay, other vertical beds of sand and clay, one 

 of which corresponds in its fossils and other characters with the 

 blue clay containing aptaria, usually known by the name of 

 London clay. Mr. Webster supposes that these vertical beds 

 were originally horizontal, and elevated, by some unknown 

 means, after the formation of the London clay. 



If a line in the direction of the central ridge of the Isle of 

 Wight be extended westwards into Dorsetshire, it will be found 

 to coincide nearly with the direction of a ridge running from 

 Handfast Point to Lulworth, and with that already described. It 

 may therefore be considered as a continuation of it. The nearest 

 tract of chalk to the north of this ridge is the South Downs ; the 

 strata of which, together with their superimposed beds, up to the 

 London clay, dip gently to the south. Hence the space between 

 may be considered as a great basin or hollow, occasioned pro- 

 bably by the rupture and subsidence of strata originally hori- 

 zontal. Within this basin, at its southern edge, that is, on the 

 northern coast of the Isle of Wight, occurs a large mass of 

 horizontal strata, in many parts visibly resting on the edges of 



