38 THE GEOLOGICAL AGE OF CENTRAL AND WEST CORNWALL. 



as " curving round" the granite masses, and a map of tlie strike 

 of the Cornish Rocks has been published, * in which they are 

 represented as folding around the various masses in such a way 

 as to frequently indicate several miles of horizontal displace- 

 ment of the stratified rocks. Nothing could be farther from the 

 truth. That the granite sends veins into the killas at the 

 junctions of the two rocks is of course well-known. It is also 

 a fact that where the junction happens to coincide with the 

 strike of the killas, this is sometimes tilted up at high angles ; 

 but very frequently, as at Gligga, Trethowel, Wheal Burn, 

 Ponsanooth, and many other places, the granite — in its last 

 movement at any rate — has been as it were punched up through 

 the killas,- carrying upon its back thick masses of stratified rocks 

 which have since been denuded away. The strike of the rocks 

 is indeed very rarely altered by the intruding masses — it is only 

 different near the granite from what is observable at some 

 distance off because the older rocks are there brought up to the 

 surface by the general upheavals which no doubt preceded the 

 actual granitic extrusions. The annexed figure shews (Fig. 7, 

 Plate B) how entirely unaffected is the strike of the killas by 

 the granitic mass of Carn Menelez, at Ponsonooth. Similar 

 examples might be given by dozens. 



As these comparatively large masses have so little effect in 

 altering the strike of the sedimentary rocks, it was not to be 

 expected that the elvan porpliyries would have any efi'ect on the 

 strike — as they only occupy fissures. In a majority of cases 

 these elvans run nearly parallel with the strike, but either with 

 a higher or an opposite dip. In a few cases, however, they cut 

 across the beds neai'ly at right angles with the strike. 



The various trappean rocks, usually if not always much older 

 than the granites, have most frequently been pushed between 

 the beds, often for several miles together — and are only occasion- 

 ally seen to cross them distinctly.! This different mode of 



* Trans. Roy. Geol. Soc. Corn. vol. vii. 



f That tliey were so thrust between the beds aud not poured over them 

 is further evidenced, by the fact that there is no perceptible difference in the 

 alterations of the beds lying above and those lying below the masses in 

 question. 



