172 Reviews — A. Strahan — Geology of Purbeck ^ Weymouth. 



gravels of Portland Island, is led to take exception to the 

 " interesting but erroneous speculation of Prestwich as to the 

 age of the great topographical features of the district." The 

 Broadway anticline, for instance, was of earlier age than sup- 

 posed by Prestwich, " for its crest was planed off before the 

 Upper Grreensand was deposited." Of course, no work on the 

 Weymouth district would be complete without a dissertation on 

 the Chesil Beach, speculations as to the origin of which have 

 given rise, he says, to a voluminous literature. To us it always 

 seemed that the papers written by Sir John Coode in 1853 are 

 by far the most valuable contributions to the subject. But the 

 suggestion of the possible derivation of the quart zites and other 

 far-travelled stones of doubtful origin from the destruction of the 

 Plateau gravels of the more immediate district is one worthy of 

 attention. 



Probably the most important part of this memoir is that dealing 

 with faults and disturbances. Ever since the days of Webster 

 and Sir Henry Englefield, in the early years of this century, the 

 coast-sections of East Dorset, in continuation of those of the Isle 

 of Wight, have attracted the attention alike of artists and 

 stratigraphists. We are favoured with a new interpretation of the 

 origin of the phenomena which are so conspicuously displayed in 

 Ballard Cliff, where the Isle of Purbeck fault first comes under 

 notice (see plate iv). The same explanation is also held applicable 

 further westwards, viz., the horizontal thrust movement, whereby 

 the Chalk has been ruptured and pushed over itself, in a manner 

 not unlike that displayed by the thrust-planes of the North- West 

 Highlands. 



Evidence is also adduced to show that the several disturbances 

 are referable to different periods. The post- Cretaceous movements 

 are thought to indicate three steps — 



1. Between Chalk and Eocene. 



2. Between Lower and Middle Eocene. 



3. Miocene and early Pliocene. 



Of course, it goes without saying that the denudation consequent 

 on the upheaval of the Chalk must have been progressing for 

 ages before any Eocene beds were laid down in this part of 

 the world, since Chalk-fliuts had been churned into pebbles 

 on many a shingle bank as the waste went on, and these same 

 pebbles form no inconsiderable portion of the Lower Tertiaries 

 all over the South of England. The movements between Lower 

 and Middle Eocene seem to be more special to their district. 

 Then came the folding of the Miocene age, to which the bulk of 

 the phenomena may be ascribed. The pre - Cretaceous, or, as 

 Mr. Strahan calls them, the intra- Cretaceous, movements, which 

 do not affect the beds above the Gault-Greensand, have already 

 been mentioned in connection with the Weymouth district. 



Though the Isle of Purbeck fault intersects the cliff again 

 west of Lulworth, its form is clearly shown in Ballard Point 



