Geology of the Neighbourhood of Weymouth, ^c. 3 



the chalk downs; on the south by Abbotsbury Castle, and a lower range which 

 slopes from thence continuously to Burton Castle ; on the west it is separated 

 by some hills of moderate elevation from the valley of Bridport. 



Of the Vale of Weymouth the following- are the three most prominent 

 features : — 



1st, The lofty escarpment of the Ridgeway which bounds it on the north, 

 running nearly in a straight line about twelve miles from east to west. 



2nd, The elevated and inclined plane of limestone which constitutes the 

 Isle of Portland, and terminates this district towards the south. 



3rd, Between this elevated Ridgeway and Portland is a space somewhat 

 triangular, composed of an alternation of low and nearly parallel, narrow 

 ridges and narrow valleys, which are terminated successively on the west by 

 the Chesil Bank, and on the east by Portland Road and Weymouth Bay ; 

 these all diminish in length successively, as their position is nearer to the 

 south, until the most southerly of them terminates in the sea at Portland 

 Ferry. 



These ridges and valleys constitute a series of narrow belts, which are 

 crossed nearly at right angles by the road from Dorchester to Weymouth ; we 

 shall therefore designate these belts by the names of the villages that stand 

 upon or nearest to them : thus the names of Upway, Upway Street, Broad- 

 way, Nottington, and Radipole, will indicate five successive belts, composed 

 of five distinct and successive formations; namely, Portland stone, Kimmeridge 

 clay, Oxford oolite, Oxford clay, and forest marble, — all dipping north towards 

 the base of the escarpment of the Ridgeway chalk : nearly in the centre of 

 this belt of forest marble the dip changes suddenly towards the south ; and 

 the same succession of strata is repeated, dipping in an opposite direction 

 southwards, and disposed in corresponding belts, which may be designated 

 by the names of Melcombe, Wyke Regis, Portland Perry, and Portland 

 Island. The formations superior to the Portland beds, if they exist south of 

 the island, are covered by the sea exterior to the Bill of Portland. At the 

 Race of Portland the agitation of the water is caused by the obstruction 

 which the subjacent mass of Portland stone offers to the tidal currents. The 

 line of section fig. I,* exhibits the general structure of this district. 



The forest marble f, with its clays and cornbrash, constituting the lowest 

 strata which rise to the surface, forms a double, central belt, elevated, as Mr. 



* Plate II. 



t The forest marble and cornbrash are so closely united throughout this district, that, except 

 in cases of minute local description, it will be most convenient to include them and their subor- 

 dinate clays under the common appellation of forest marble. 



B 2 



