170 Revieivs — A. Strahan — Geology of Parhech 8f Weymouth. 



Of the many curious features which the Lower Purbeck present, 

 that of ' brecciation ' has caused not a little diiferenoe of opinion. 

 Mr. Strahan is inclined to support the view propounded by the 

 Rev. 0. Fisher, that the fracturing of the ' broken beds ' was due 

 to their having been deposited over a mass of decaying trees and 

 mosses and having subsequently fallen in. Plate iii gives a good 

 representation of the 'broken beds' near Lulworth, and may also 

 be taken generally as a favourable specimen of the application of 

 photography to stratigraphical features. 



The Wealden Beds in this area are not particularly interesting 

 from a paleeontological point of view, though at Worbarrow Bay 

 their total thickness is stated to be 1,237 feet, the formation be- 

 coming thinner westwards. The Lower Greensand is exposed in 

 three coast sections, viz., at Punfield Cove in Swanage Bay, in 

 Worbarrow Bay, and in Mupe Bay, westward of which it thins 

 out. As already determined in the " Geology of the Isle of Wight," 

 the author accepts Mr. Meyer's opinion that the Punfield Beds of 

 the Isle of Purbeck are Lower Greensand ; he states also that the 

 subdivisions of the Isle of Wight, though greatly attenuated, are 

 partly recognizable at Punfield, where the total thickness is 198 feet. 

 At Worbarrow Bay the section shows 136 feet, and the beds are less 

 fossiliferous. Of the few inland exposures of Lower Greensand the 

 Corfe Castle cutting alone exhibited any points of interest. 



The Gault and Upper Greensand, owing to a change in the 

 character of the former, are not to be separated within the district. 

 Like the rest of the Cretaceous rocks, the Gault and Greensand are 

 thinner in Purbeck than in the Isle of Wight, but unlike the others 

 they thicken again further west. Palgeontologically, these strata 

 are divided by Dr. Barrois into the zones of Pecten asper and 

 Ammonites inflatus, but the lithology does not quite correspond 

 with the zoning. At Worbarrow Bay this formation is 167 feet 

 thick. A fine series of fossils appears to have been collected by 

 Barrois from the Upper Greensand of Durdle and Lulworth. 



The Chalk, being one of the most important formations within the 

 area, is dealt with at considerable length, and the figures of fossils 

 are rather more successful than has been the case in some of the 

 previous memoirs. Dr. Barrois' paleeontological zones of the Chalk 

 of South Dorset are given in a table (p. 166), and on the following 

 page Mr. Strahan gives us his latest views on the subdivisions of tlie 

 Chalk as displayed in Ballard Cliff: — 



Ft. in. 

 Upper ( Chalk with flints 



p I Massive but somewhat lumpy chalk, without flints 



( Chalk Rock : a layer of very hard green-coated nodules 



IHard, rough, and lumpy chalk 

 Smooth, thick-bedded cbalk, with partings of marl ... 

 Melbourne Eock ; rough, nodular, and flaky chalk, with sparry 

 joints 6 



20 











4 



6 







90 







