UPPER GREENSAND. 71 



to Calbourne where the Chloritic Marl, 14 feet 2 inches thick, 

 abounds with phosphatised Ammonites. The Chert Beds appear 

 also, but the greater part of the Malm Rock is concealed by a 

 thick stratified talus of chalk. 



Proceeding eastwards we find the Chert Beds at Coombe Tower 

 beginning to form the feature, which becomes so conspicuous in 

 the central and southern parts of the Island. In this neighbour- 

 hood the chert, white in colour and accompanied with much 

 chalcedony, is exposed repeatedly all along the crest of the 

 escarpment to Shorwell, where it is quarried, or rather dug, for 

 building. 



East of SI\orwell the escarpment becomes steadily bolder, and 

 we find blue chert associated with the white alono- the crest of the 

 hill. At the east end of this hill, over the Chillerton road, free- 

 stone is worked in a quarry below the Chert Beds, this being the 

 most westerly appearance of the bed so prominent about Yentnor. 



Between the bold escarpment of Rams Down and the Chalk 

 Downs runs the long winding valley of Chillerton Street, a slight 

 prolongation of which would convert the Chert Beds of Rams 

 Down into an outlier. This valley owes its existence to some 

 springs issuing at the junction of the Greensand and Gault, along 

 the line of a gentle syncline, which is indicated by the relative 

 dips in Rams Down (from 4° to 5°), and in the nearly horizontal 

 Chalk. The trough becomes more marked near Sheat, and in 

 Gossard Hill.* Near the former place the Malm Rock dips 

 north-east at 10°, and tlie Gault, striking right across the valley 

 of the Medina, runs for nearly a mile eastwards around Rookley, 

 while on the top of the shoulder thus formed, an outlier of Upper 

 Greensand makes a narrow ridge, capped with chert and striking 

 nearly due east and west, with a dip to the north of 8° to 10°. 

 The north side of the syncline is not well defined, as the beds 

 gradually assume a horizontal position. It might perhaps be more 

 correctly described as a monocline, like that of the central axis of 

 the Island, but on a small scale. (^See also Horizontal Sections, 

 Sheet 43, No. 2.) 



Numerous old quarries in the Chert Beds and underlying 

 freestone roughen the brow of the hill above Gatcombe and 

 Whitcombe. On mounting this eminence, we find a long dip- 

 slope stretching away westwards to the boundary of the Chalk 

 Downs, which is generally marked by a rise in the ground. 



In the valley of the Medina near Shide the Upper Greensand 

 disappears from sight till we reach Great East Standen. In two 

 large pits, however, long since completely overgrown, between West 

 Standen and Great East Standen, " malm " is reported to have 

 been dug. So far as can be judged the pits have been opened in 

 the lowest beds of the Chalk Marl. 



At Arreton, while the topographical feature of the Upper Green- 

 sand is well marked, the Chert Beds no longer form as definite a 

 subdivision as heretofore. The stony bands, to which this feature is 



* A bold hiU near Rookley, so named in the old edition of the Ordnance Map. 



