CORNISH POST-TERTIARY GEOLOGY. 13 



(Plate, Fig. 2.) Section C is nearly 45 cliains from the Beacon, 

 in the direction of N. 29° W. 



Soil and overburdea 5ft. 9in. 



Sandy overburden 1ft. lin. 



Fireclay 6ft. 2in. 



Sand 7ft. Oin. 



Sandstone on sand 2ft. Oin. 



Waterworn rock. 

 (Plate, Fig. 3.) Section E is 41 chains from the Beacon, in the 

 direction of N. 11° E. 



Soil and overburden 6ft. lOin. 



Candle clay 1ft. Sin. 



Sand 14ft. Sin. 



Sandstone oft. lOin. 



Sand Oft. 4in. 



Ou waterworn rock. 

 (Plate, Fig. 4.) Section F is 16^ chains from the Beacon, in the 

 direction of N. 9° E. It shows a cliff as laid open in mining 

 operations at Wheal Coit. The cliff facing north was first exposed, 

 and a level was then driven into it southwards (dotted line), when 

 sand was again found. " From which," says Mr. Davies, " it may 

 be concluded that we have here a wedge-shaped promontory from 

 the main cliff to the west." 



Soil 2ft. Oin. 



Overburden 20ft. Oin. 



Bluish-grey candle clay to 2ft. Oin. 



Sand, with pebbles and boulders of granite and stream tin ore 2 to 7ft. Oin. 



On waterworn Killas rock. 

 The candle clay is bluish, plastic, adhesive, and very tough. The 

 fire clay is bluish or yellowish, is coarse through admixture of sand 

 and gravel, but yields candle clay when well washed. The sand is 

 nearly pure silica, the grains being perfectly i-ounded and polished. 

 Its colour is in most cases removable by washing. The sandstone 

 is produced by cementing oxide of iron, and occurs sometimes in 

 cores with a sand centre, sometimes in flat uneven layers. The 

 pebbles vary from the size of a hazel nut to large boulders " weigh- 

 ing a ton or more." They are all from local rocks, and " vary with 

 the different districts, and may often be referred to the rock above 

 which they lie." 



The variability and impersistence of the beds may be still further 

 seen from the following sections, which I obtained on the occasion 

 of my visit. 



