144 Correspondence — Mr. Jukes- Browne — Mr. Kinahan. 



than with any other known European Pre-Cambrian group, 

 especially as he found them overlaid unconformably by rocks similar 

 to those found in the Pebidian group. Certainly from his descrip- 

 tions they could not be classed with the dark hornblendic and red 

 gneisses which the Scotch geologists have invariably claimed to be 

 characteristic of the Hebridean or Lewisian group. Moreover, the 

 very fact that most of the gneisses in the central highlands were 

 found, like the Dimetian of Wales, to be highly quartzose in 

 character, formed one of the chief stumbling-blocks to their being 

 recognized as of Pre-Cambrian age : even Nicol found this a difficulty. 

 Now, however, since the Dimetian rocks in Wales have been recog- 

 nised, this need offer no difficulty in future, and I feel convinced 

 that ere long the Dimetian and Pebidian groups will be as easily 

 separated from one another even 'in Scotland as has been the case 

 now in Bohemia through Mr. Marr's researches. 



Hendon, N.W., Feb. 7, 1881. H. HiCKS. • 



DISTTJEBANCES IN THE CHALK OF NOEFOLK. 



Sir, — I am indebted to Mr. H. B. Woodward for pointing out that 

 Mr. J. E. Taylor was subsequently inclined to suggest a different 

 age and cause for the disturbance at Whitlingham. This had 

 escaped my notice, but supposing that Mr. Taylor's later view, now 

 endorsed by Mr. Woodward, is correct, it does not follow that all 

 disturbances of the Chalk in Norfolk are due to the same cause. 

 The passage of ice has no doubt disturbed and broken up the Chalk 

 in many places ; but I still submit that it is difficult to conceive of 

 any surface agency being capable of producing such a sharp con- 

 tortion in a solid scar of chalk like that at Trimmingham. 



A. J. Jukes-Browne. 



HiGHGATE, Feb. 4. 



SHEINKAGE FISSUEES. 



Sir, — I would direct the special attention of geologists to the 

 chasms due to the subsidence in Cheshire ; of which an excellent 

 sketch recently appeared in the Graphic. From these shrinkage 

 fissures we learn how gorges or canons can be made without 

 denudation— because if such a small thing as the vacancy in a salt 

 mine produces such marked results, how much greater must be the 

 results from vacancies caused by vulcanicity and other natural 

 phenomena? The sketch has an aspect very similar to some of 

 the maps of canons in Dr. Hayden's magnificent reports. 



G. H. Kinahan. 



We regret to record the death of two well-known and highly- 

 esteemed geologists, namely : — Dr. J. J. Bigsby, E.E.S., F.Gr.S. ; 

 and Prof. James Tennant, F.G.S. Notices of these veterans will be 

 given next month. 



