J. C. Mansel-Pleydell — Geology of Dorset. 441 



westerly direction from Frome Vanchnrch through Toller to Ched- 

 dingtoii; that of the lesser from Wraxall to Melbury. The outliers 

 of Pillesdon, Lambert Castle, Stonebarrow Hill, Golden Cap, and 

 Eype Down, form the most western representatives of the series. 

 It flanks the great Oolitic vale of Blackmore from Melbury to 

 Shaftesbury with only one interruption at Buck] and Newton. At 

 Lyon's Gate a spur of the series takes a southerly direction, and 

 occupies a narrow valley to Cerne Abbas ; small outliers occur at 

 Sydling, Holcombe, and Hilton. 



The Chloritic Marls at the base of the Chalk-range which bounds 

 the southern and eastern sides of the Vale of Blackmore and the 

 Anstey valle}'- are very fossiliferous ; the uppermost bed, consisting 

 of an argillaceous limestone, is characterized by the Cephalopod 

 Scaphites cBgualis ; its principal development is at Chard, Monckton, 

 Cranborne, and Chaldon, where it does not exceed eighteen inches 

 in thickness. 



In the palasontological collection of the British Museum is the 

 stem of a tree-fern, Cavlopteris punctatus, from the neighbourhood 

 of Shaftesbury ; it is a cast in sandstone, and exhibits indications of 

 alternation of climate, or seasonal interruptions to its growth.^ 



Uppek White Chalk with Flints. — A marine formation of great 

 thickness, consisting of nearly pure carbonate of lime precipitated 

 and deposited at the bottom of the sea, and in some cases consisting 

 of from ninety to ninety-five per cent, of Foraminifera. The differ- 

 ence between the Upper and Lower Chalk is the absence of flints in 

 the latter ; there are fossils special to each division, most of which 

 evidence deep-sea conditions. 



- Denudation has been actively carried on wherever the Chalk 

 formation exists in Dorsetshire, but owing to the absence of definite 

 marks indicating any particular horizon, it is difficult to determine 

 its relative position. The beds of flints which cover extensive tracts 

 of Chalk containing undisturbed layers of flint, afford evidence not 

 only of the immense thickness of the original mass, but also of the 

 enormous amount of material which has been removed. The whole 

 group may be viewed as one continuous series, with a Fauna which 

 varies no more than might be expected from the varied circumstances 

 of its deposition through a lapse of ages. The beds rise at Chil- 

 combe with a bold escarpment characteristic of the formation ; from 

 Chilcombe Hill east of Bridport to Lul worth, whence it is contracted 

 into a narrow elevated isthmus, to Ballard Down, which divides 

 Swanage and Studland Bays. The most southern extension is on 

 the west side of the county south of the village of Abbotsbury, its 

 northern boundary flanks the vale of Melbury, and with various 

 undulations towers over the Vale of Blackmore from Minterne to 

 Shaftesbury, and continues conterminous with Wiltshire, from thence 

 to Boveridge, where it takes a southerly direction to Wimborne, and 

 westerly to Bere Regis, the Woolwich and Reading Beds reposing 

 on it. From Corscombe to Shaftesbury it rests exclusively on the 



1 See paper by Mr. W. Carruthers in Geol. Mag., 1865, Vol. II. p. 484, PI. XIII. 

 Fig. A. 



