522 Correspondence. 



lava-cnrrents, great sheets of which may be seen descending to the 

 sea-shore, where they are sometimes thrown up in rugged masses, 

 as though acted on by the sea-water when in a state of fusion, as 

 may now be seen in Sicily. 



Next to these most ancient rocks come the lower hills, whose origin 

 we assign to a somewhat later period, when the volcanic action was 

 dying out : these are composed of materials readily acted on by the 

 atmosphere, and are thus shaven into cones. I must now refer to the 

 trap dykes. Every geologist who has studied the Western Highlands 

 well knows the great area which has been subjected to volcanic action 

 at a comparatively late period. In the low grounds, in the beds of 

 rivers, and on the sea shore, we find trap-dykes, from one inch to 

 several feet in width, passing through the more ancient beds, into 

 which various qualities of trap have been injected. This appears to 

 me to have been the subsiding action of the great elevatory force, 

 and it is interesting to find it extending in Scotland up to the Ter- 

 tiary period, for Skye offers at Broadford most interesting examples 

 of trap-dykes traversing the Lias limestone. 



I will only add, that subsequently to the periods referred to, came 

 that universal surface action by which all Scotland and the North of 

 England have been covered with gravel beds — a subject deserving 

 deep and persistent enquiry. In these beds the primeval forest 

 grew, which, in its turn, has been buried beneath peat or soil, the 

 surface of which is now adorned with the flora of our modern time. 



Yours, 



Thos. C. Bkown. 

 Ftjether Barton, Cieencester, 

 1th September, 1867. 



THE ORIGIN OF GRANITE. 

 To the Editor of the Gteological Magazine. 



SiE, — I am glad to see ''the origin of granite" is likely to crop 

 up as a result of Dr. Sterry Hunt's Lecture " On the Chemistry of 

 the Primeval Earth," which has been so ably commented on in the 

 last number of the Geological Magazine by Mr. David Forbes. 

 There has been so much "Denudation" of late, both marine and 

 atmospheric, that we need not be surprised if a deep-seated rock, 

 like granite, is laid bare, and at last appears on the surface in the 

 field of geological discussion. 



At the recent meeting of the British Association in Dundee, Pro- 

 fessor Ansted communicated a paper " On the Conversion of Strati- 

 fied Eock into Granite in the North of Corsica." I took part in the 

 discussion which ensued ; but as my remarks, together with those of 

 Sir Charles LyeU and Mr. Geikie, were reported thus — " Some dis- 

 cussion followed the reading of the paper," while those of Professors 

 Phillips and Eamsay were merely noticed, I venture to ask you to 

 have the kindness to permit me to re-state in the pages of the 

 Geological Magazine, as briefly as possible, the substance of what 

 I said on that occasion. 



