246 Dr. FiTTON on the Strata below the Chalk. 



(128.) Upper Green-sand. — The effect of the unequal inclination of the 

 two sides of the valley is remarkably shown by the great difference in the 

 extent of the spaces occupied by this formation. On the souths the upper 

 beds are concealed at the foot of the chalk hills ; but the lower strata shoot 

 out into plateaus^ which form the tops of the hills all the way to Shaftes- 

 bury ; but on the north the whole series of the Upper green-sand rises ab- 

 ruptly and forms a very narrow ridge of unequal height. The Map and Sec- 

 tions^ Plates VII. fig. 3. and X. a., No. 13., sufficiently explain this structure. 



Some of the best sections of the transition from the chalk into the Upper green-sand are 

 visible near Barford St. Martin and thence to Baverstock. In the lane over Baverstock Hill 

 (called in the country Cloudles) the series consists of alternate beds of chalk and sand with 

 green particles, succeeded by a thick bed of green-sand abounding remarkably in Gryphcea vesi- 

 culosa, which can be traced almost entirely round the valley. The ridge of these sands over 

 Dinton House is full 200 feet above the bottom of the depression between it and the lowest 

 chalk. 



The greatest superficial extent of this formation occurs in the vicinity of Shaftesbury, where 

 the upper part seems to have been better preserved than in the continuation of it eastward. The 

 sections vary from 50 to 60 feet in thickness ; of which about a third at top contains beds of 

 chert like those of the Isle of Wight : but the lower beds only are found in the plateaus which 

 project beyond the chalk. 



Several good sections of the upper strata are visible in the lanes about Shaftesbury ; — at Lud- 

 well, Hernsham Street, in the ascent from Brookwater, and thence to the foot of White Sheet 

 Hill, where some of the quarries include chert and veins of chalcedony. 



From Castleditches, — an ancient fort or encampment on the summit of a remarkable promi- 

 nence, the sand which composes the top declines uniformly towards the foot of the chalk range, but 

 extends with an even surface, westward to Shaftesbury, and eastward to Barford Heath. The beds 

 have many points of general resemblance to the sands of Blackdown; — with this important dif- 

 ference, that a very distinct stratum of bluish clay (Gault), which is wanting at Blackdown, is 

 here found, everywhere, below the sand. 



The relations of these strata are well shown in a large quarry at the top of the hill east of 

 the valley of Fovant and of the Pembroke Arms, where the following was the order : — 



Fovant Quarry. 



^ Ft. In. 



Soil and Grass. 



1. Greenish sand, alternating with gray, including stone which passes into chert, in irre-1 ,„ 



gular concretional bands and masses : — very like the sands of Blackdown .... 14 to J 



2. Sand of a much darker hue, below passing into stone about 5 6 



.^. Stone called "Greenstone", in firm beds, whichare quarried for building; upper surface 1 ^ 



irregular ; contains Gryphcea vesiculosa, Pectens, and shark's teeth about j 



This stone is valuable from its not being affected by frost. It can therefore be dug 

 at any season, and stands well in water, as the foundations of bridges, and in 

 exposed situations, as in copings, &c. 



4. Stone ; but not good 1 6 



5. Sand ; depth unknown. 



On the north of the valley, the Upper green-sand appears likewise to consist of two portions ; 



