Dr. PiTTON on the Strata below the Chalk. 235 



its thickness only at 100 feet, the total thickness of the whole of the green-sand group would not 

 be more than 300 feet : the actual tliickness of the sands being nearly 200 feet at Lyme Regis ; 

 and at Whitecliff, according to my own measurement (it is not stated by Mr. De la Beche), 

 about 160. The beds below this cherty group represent Mr. De la Beche's " Fox mould " (No. G. 

 of the above list) ; and are apparently the equivalent of the upper and more ferruginous group 

 of the lower green-sand : the lower, moist, and dark-coloured sands, with the " cowstones" at 

 the bottom, being probably the equivalent of the middle, dark, cohesive sand of Sandgate (24.), 

 Shanklin (192.), and Black -gang Chine (195.); — the "cowstones" representing the calcareous 

 •rroup of Hythe, &c. This occurrence of nodules dispersed in sand is frequent wherever calcareous 

 strata are near their termination ; as in the cases of the Portland stone, the lower oolite, &c. 



I have stated these resemblances that the whole case may be before the reader : but in the vale 

 of Wardour, — where the distinct occurrence of a bed of blue clay with the characteristic fossils 

 of the gault, leaves no doubt as to the place where the sands are divided, — the inferior beds 

 of the Upper green-sand acquire a character very like that of the Lower in other places ; and 

 the latter is either wholly wanting, or very imperfectly represented. 



(119.) Blackdown Hills. — In approaching the hills of green-sand, their 

 aspect on every side is the same, precisely resembling- that of the long- flat- 

 topped ranges of this formation, and of the Bagshot sands, in Kent, Surrey, 

 and Hampshire. The surface is barren, and the chief products, at present, 

 seem to be furze and heath ; though in former times, it is reported, extensive 

 woods were here. 1 ascended first from Wellington on the north of the 

 Blackdown Hills, and found red marl for more than two thirds of the height, 

 so nearly resembling some of the sandy and variegated clays of the Wealden, 

 especially of the Hastings sands, that but for the presence of sulphate of 

 lime in crystalline nests, it would be difficult to distinguish them ; while the 

 greenish varieties of the marl also very much resemble some of the beds above 

 the chalk in the Isle of Wight. From Beacon Hill, on the south-west of 

 Wellington, the uniform level of the summits is very striking, the eye being- 

 carried over the whole range without interruption, and the ravines quite lost 

 sight of. The absence of the remains of chalk from the debris on the top of 

 these hills is remarkable : I searched long, but did not see a single fragment 

 of flint, all those which I could find being chert, easily distinguishable from 

 chalk flints. In the yellowish sand near the surface, at the Barnscombe side 

 of the hill, brown iron ore is found, in polished fragments of very high lustre, 

 resembling those of the lower green-sand at Sandown Bay in the Isle ol 

 Wight (1200 ; p. 188.), of Surrey (39.), and Western Sussex. 



Although the strata forming these hills are in a general view continuous, the whole country is 

 divided by fissures, attended in some cases with considerable dislocation ; for an account of 

 which I refer to Mr. De la Beche's Map of Devonshire, and his essays on Theoretical Geology *. 



* " Researches in Theoretical Geology," 1834, p. 185, &c. 



