TERTIARY STRATA IN THE ISLE OF WIGHT. 



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the state of marl, and are used as manure. This formation is char- 

 acterised by containing, exclusively, freshwater and land shells, sim- 

 ilar to what are found in the neighbouring marshes ; they belong to a 

 small number of genera or species, being chiefly lymnites, planorbes, 

 turbinated shells, (allied to ceriihea,) cyclostomas, and helices. 



Having described the tertiary strata round Paris and London, I 

 shall proceed to the tertiary strata in the Isle of Wight, which con- 

 tain many beds that are wanting in the London strata. The forma- 

 tions of the north of France and of England, do not, as it was once 

 imagined, compose the whole of the tertiary deposits, but only the 

 lower and middle parts. A brief account of the tertiary formations, 

 in other countries, will be subsequently given. 



For the first accurate account of the tertiary strata in England, we 

 are indebted to Mr. Webster, who published, in vol. ii. of the Tran- 

 sactions of the Geological Society of London, a description of these 

 strata in the Isle of Wight, and their connection with the subjacent 

 chalk. The chalk, covered by the London clay, passes under the 

 channel, called the Solent, and rises in the middle of the island, 

 forming a range of hills which extends from Culver Cliffs on the 

 east, to the Needles on the west. Here we meet with a remarka- 

 ble derangement of the beds of chalk, and of the superior strata ; 

 part of the strata of this range of hills from the western to the east- 

 ern side of the island are thrown into a position nearly vertical, evin- 

 cing the action of a mighty disturbing force, which can be so often 

 observed to have broken or upheaved the secondary and tertiary 

 strata, in the vicinity of the Alps. Evidence of the same dislocation 

 of the strata, extends from the Isle of Wight into Dorsetshire. 



The whole thickness of the beds at Alum Bay, in the Isle of Wight, 

 which are nearly vertical, comprising fourteen hundred and eighty 

 one feet of strata above the chalk, about nine hundred and eighty 

 seven feet of chalk, and five or six hundred feet of lower strata, is 

 according to Mr. Webster's measurement, not less than three thou- 

 sand feet. Farther south the strata under chalk are seen again in 

 their original horizontal position ; and on the northern side, there are 

 hills composed of horizontal strata, evidently of a formation posterior 

 to the time when the chalk strata were overturned. That the latter 

 were once nearly horizontal, m.ay be inferred from their generally oc- 

 I curring in that position in the southern counties, and this conclusion 

 I is rendered certain, from the following circumstance, described by 

 Mr. Webster. In one of the vertical beds consisting of loose sand 

 are several layers of flints, extending from the bottom to the top of 

 the cliff. " These flints have been rounded by attrition, are from an 

 inch to eight inches in diameter, and appear to have belonged to the 

 chalk. Now it is inconceivable that these flints could have been 

 originally deposited in their present position : they distinctly point 

 out the former horizontal direction of this series. There are no 



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