EAISKD BEACHES. 419 



It is well that the study of geological phenomena is not 

 confined by local limitations, for immediately beyond the 

 boundary of our county, and over the surface of the limestone 

 district on the south and east of Plymouth, the superficial 

 deposits have been opened up to our observation by quarrying, 

 more fully than in any other such limited area in the south of 

 England, presenting most instructive vertical sections of the lime- 

 stone beds, and horizontal exposures of the surface diluvial 

 deposits. 



In area the limestones extend from the Hamoaze on the 

 west, through the towns of Devonport and Plymouth to West 

 Sherford on the east, a distance of six miles, with an average 

 width of three quarters of a mile. The strike of the beds is 

 east and west, and the general dip from 40° to 80° south. Some 

 of the beds, mainly at their northern limit, are bent — curved and 

 upset, especially near Pomphlet ; and at the northern limit of 

 the Oreston Quarry, ' there is an almost vertical exposure of 

 of Slikenside, showing the great pressure arising from the slipping 

 of one bed over another. A further remarkable feature of these 

 limestone beds, is the large amount and size of their jointed 

 structure. These joints may be seen in all the quarries, cutting 

 across the strike- of the beds at nearly regidar intervals through 

 a nearly perpendicular height of from 50 to 100 feet and of a 

 width of from a few inches to 1 or 2 feet ; and where the beds are 

 most disturbed, into cavernous open cavities, some partially and 

 others completely filled with diluvial boulders, sand, and rain- 

 wash. The general direction of the joints is N.W., or more 

 particularly 20'^ W. of N., being the present variation of the 

 magnetic compass. And the caverns at Oreston, Pomphlet, and 

 Cattdown, all run on these lines of joints, and must be recog- 

 nised as natural cavities. 



In July, 1875, I found on the western crest of the Hoe a 

 considerable excavation showing the following section : — 



1. A brown friable surface soil about one foot thick. 



2. Boulders and pebbles in a confused matrix of sand and 

 clay, of a variable depth of from one to four feet. The stones 

 were mainly quartz, with others of blue grit and altered slate 



