112 Mr. P. I. Martin's Observations on the Anticlinal Line 



and that a double system of valleys and a particular line of 

 drainage remained, as evidence of the fact, proper allowance 

 being made for a contemporaneous or immediately consecutive 

 diluvian action. 



Fortunately for this theory, the greater part of it had been 

 already made out by Dr. Buckland in the paper above al- 

 luded to*; and a double system of valleys, or the transverse 

 sections of the chalk escarpments, which 1 have ventured to 

 call " river fissures," made the medium of drainage, had been 

 observed by Mr. Conybeare. I may also acknowledge in 

 this place, that my observations upon Portsdown Hill, as a 

 chalk outlier-by-protrusion, have been in part anticipated by 

 the latter gentlemanf, although he supposes it to originate 

 in a simple undulation of the surface of the chalk, anterior to 

 the aera of deposit of the higher strata. This is the notion 

 apparently also of Mr. Webster, who, in his illustrative map 

 in the second volume of the Geological Transactions, has 

 connected its eastern extremity with the chalk of the South 

 . Downs. Protrusion presents itself every where in such close 

 connection with denudation, and plays so large a part in the 

 modification of all parts of the surface of the earth, that its 

 recognition in all formations, from the highest to the lowest, 

 cannot be too ample. 



The anticlinal line which separates the two English Basins, 

 commences near Devizes, or in the Vale of Pewsey, and ele- 

 vates and causes the exposure of the great expanse of chalk 

 which is discovered between the tertiary formations north and 

 south of it +. Quitting the chalk in the Alton-Hills, it brings 

 up the greensand or glauconite, in which it is continued on 

 into Sussex. Fi'om the glauconite, at the head of the Weald 

 Valley, it raises in succession the various beds of the Weald 

 formation, or " Wealden," and crossing the Channel, gives 

 rise to the denudation of the Boulonnois, and is finally lost in 

 the chalk of Picardy ; unless, which is very probable, it there 

 assists to separate the tertiary formations of the Paris Basin 

 from those of the eastern extremity of the London Basin, 

 after it sinks under the North Sea. 



In this course of about 200 miles, in a direct line east and 

 west, or a little inclining to south-east and north-west, it presents 



* Geol. Trans, vol. ii. New Series. 



t Outlines of the Geology of England and Wales, Part I. p. 82. 



X The great chalk dome of Hampshire and Wilts is in the line of eleva- 

 tion ; but it is probable that more precise marks of dislocation may be 

 traced in the line of country between Farnham and Devizes; forming a 

 chain of valleys of which the Vale of Kingsclcre is a part, and bringing 

 the great eastern denudation into more strict relation with the western. 



everywhere 



