Correspondence. 573 



PEOFESSOR JUKES ON THE DEVONIAN E0CK3. 

 To the Editor of the Geological Magazine. 



SiK, — In his recent communication to the Geological Society, on 

 November 7th, Professor Jukes argues that the rocks of North Devon 

 are identical with the Carboniferous and Old Eed Sandstone rocks of 

 the South of Ireland. His conclusions seem to be mainly based 

 upon great lithological similarity, and are strongly contested by 

 English Geologists, chiefly upon palgeontological grounds. It ia 

 admitted by both sides that the Devonshire rocks from the Culm 

 Measures northwards, dip steadily to the south, but the large 

 thickness thus represented is, according to Professor Jukes' view, 

 reduced by a great east and west fault along the strike allowing the 

 northern portion of the rocks to sink upon that side, and causing a belt- 

 of Old Eed Sandstone to make its appearance crossing the country 

 along with it, and producing the following order of succession : — 



South. S^ c^ \ c^^ ^' North. 



^ / ^ 



His opponents deny the existence of the fault, and look upon the 

 whole as a regular sequence of Devonian (or Old Eed) rocks, with 

 successiA'e fossiliferous zones passing upwards into the Culm 

 Measures. 



Mr. Jukes' idea, if we mistake not, has been to a certain extent, 

 in one way or another, long since advocated by some Irish Geologists, 

 who have held that plant-bearing beds in North Devon had represen- 

 tatives in the Irish Old Eed Sandstone, or at least that the Devonian 

 rocks of that district, and a large portion of the Irish Old Eed, both 

 belonged to the obsolete Greywacke formation. At all events, 

 whether the difference between the fossils of these English and Irish 

 areas be sufficient to establish a difference in their Geological nomen- 

 clature, or not, it must be remembered that the rocks of both districts 

 having a somewhat similar general strike, and a strong lithological 

 resemblance, are geographically so situated as to have been apparently 

 once connected, although the organic remains on each side of the 

 Channel differ more than might have been expected from the aspect 

 of the rocks. — Yours truly, 



London, li'ov, 9, 1866. "^ "^ "^t^' 



GLACIATION IN DEVON AND ITS BORDERS. 

 To the Editor of the Geological Magazine. 



SiE, — The Eev. 0. Fisher, in his article on "The Probable 

 Glacial Origin of Certain Phenomena of Denudation," which appears 



