THE GEOLOGICAL AGE OF CENTRAL AND "WEST CORNWALL. 193 



unless it be that known as the Maenporth Elvan, No. 46 on Mr. 

 Barnett's map — which he speaks of as " a hard, fine-grained 

 quartzo-felspathic rock, with a little mica distributed through it." 



Nos. 7 and 8. The next appearances of the mica-trap veins 

 with which we are accj^uainted, are the two bands of " greenstone " 

 marked on the survey maps as crossing Beacon Hill, between 

 Falmouth and Pemyn. Quarries were formerly open on these 

 veins on the top of the hiU — one of the pits being still open and 

 carried down to a considerable depth for the sake of a 

 magnificent vein of white quartz which crosses the trap just 

 here.* Most of the trap here is of extremely fine grain, and a 

 partial decomposition extends as far down as the bottom of 

 the pit, nevertheless the true nature of the rock is perfectly 

 evident. Both veins may be traced down to the shore beneath 

 the Greenbank terrace, where they pass under the water — to 

 re-appear on the opposite side of the creek. 



7a is a little vein occurring at Pendennis Point, of which 

 I was first informed by my friend Mr. Howard Fox. Sa occurs 

 in a quarry between Falmouth and Penryn, near Mr. Stephens's 

 rope factory. This also was first observed by Mr. Howard Fox, 

 who drew attention to the remarkable spheroidal structure 

 which particularly characterises it here, in a paper read before 

 the Miners' Association at Falmouth in 1873. 



Nos. 9 and 10. These are the apparent continuations of 

 Nos. 7 and 8 on the opposite side of the creek. No. 9, or the 

 most easterly, is very wide, and has been opened out very 

 extensively for building purposes. No. 1 is much narrower, 

 but can be traced farther, in fact it may be traced right across 

 the promontory to the Mylor creek, where it may be seen at low 

 water at a point a little west of the church. In the large 

 quarry (No. 9) the stone is a good deal decomposed, especially 

 near the surface, and full of minute cavities, owing to the 

 disappearance of one of the components ; nevertheless good 

 pieces may be obtained, from which it appears to be very tine 

 grained but of quite typical composition. 



* This vein of quai-tz is the finest and purest I have evei* seen. Perfectly 

 white, it is often seen 3 or 4 feet wide and quite free from strain or flow for spaces 

 of many inches or even feet. It has only been used for roadstone, but it would 

 be a perfect material for the manufacture of the better kinds of glass, as it is 

 almost chemically free from iron. J, H. C. 



