THE GEOLOGY OF THE ENGLISH CHANNEL. 165 



New Eed series ; it contains derived fragments of the Hand Deeps 

 gneiss and schist ; it is found side by side with them, and hence if they 

 are in situ so, too, in all probability, is it. 



The sixth line of argument for the demonstration of the local origin 

 of the rocks and pebbles is as strong as any. There are some rocks so 

 friable that they might not travel half a mile without being destroyed. 

 Many of the marls of M. 29 above referred to are of this class, the 

 ' paper shale ' of M. 53a, S. 22° W. Edd., 32 2 miles, is another rock 

 which must be content to rest at home or be destroyed. From these 

 which cannot be moved without destruction, through those which can 

 only travel a little way without disintegration, on to others which 

 may journey but must be considerably reduced in their progress and 

 l)ear evidence of their wanderings, there is a complete succession. The 

 extreme of the class may be taken to be flint, and if entirely unrolled 

 flints are found, as at M. 67, S. 19° W. Edd., lOo miles, among other 

 places, it may well be assumed that they are untravelled. 



On some one or more of these six lines of argument every class of 

 rock found in the dredgings may be shown to be practically in situ 

 at one or more stations. Its associates are arguably almost equally 

 near their points of origin, for it is impossible to attribute to any 

 drift, arising from whatever cause, the selective and confounding 

 ability to bring like to like, to transport from a distance and place 

 among its kin any stone or stones. A little exchange of material 

 between adjacent areas there must be, but we are not about to attempt 

 any geological mapping within extreme narrow limits of error. 



THE CRYSTALLINE ROCKS. 



Granites, Diorites, Gneiss, Schist, etc. 



Mr. A. E. Hunt quotes, in a paper above cited, a letter received by 

 him from the late Mr. E. B. Tawney, as follows : — 



" My views are rather Britannic ; I look to Brittany for their origin 

 [the origin of the Channel granites and gneisses, E.H.W.]. I consider 

 Brittany reached to Plymouth Sound and then stopped short, but am 

 inclined to give Start Point to it. If so, the granites are oiot all pre- 

 Devonian, though pre-Carboniferous." 



To much the same conclusion the writer has arrived, as at least a 

 working hypothesis, with the correction that some at least of the 

 Brittany granites are now commonly accepted as of Carboniferous 

 age: 



To one who has worked in a granite area such as Dartmoor there 

 is nothing unexpected, nothing disappointing in finding, as in the 

 present instance, such considerable variety among the plutonic rocks, 



