Correspondence — Air. D. Mackintosh. 47 



and Aqiiltaino, am! not to Soutlicrii Fiiuico and Switzerland, wlicro 

 tlio Gaiilt division is largely represented. 



M. Lory begs nio likewise to state tluit in liis taljidar view 

 (p. 252 of last year's Vol. of the CricoroarcAL Magazine), a simple line 

 without connecting braces sliould divide the two columns respec- 

 tively devoted to the Jura, and to Grenoljle ; that he does not believe 

 the yellow Limestone of Neuchatel to bo the erpiivalent of the 

 limestone with Cliama ammonia, but rather considers it more closely 

 connected to the ctage which underlies it. That in the 2nd column 

 the words '' corresponding to a complete change of fauna " refer 

 exclusively to tlie word "break," and not as the brace would seem 

 to imply to a scries of beds in the opposite column, and which are 

 the equivalents of the Kimmeridge clay. 



I avail myself of this opportunity to mention that, as so many of 

 my geological friends have expressed a desire that I should en- 

 deavour to comj)lete my large work on British fossil Brachiopoda 

 during the present winter, I am unavoidably compelled to postpone 

 the publication of the continuation of my "Notes on Continental 

 Geology " until the labours connected with the work above named 

 will have been completed. Thos. Davidson. 



22, Pakic Ckescent, Bkighton-, 



ME. DE EANCE & THE EEV. T. G. BONNEY ON SURFACE-GEOLOGY 

 AND LYTHODOMOUS PEEFOEATIONS. 



Sir, — I regret that Mr. De Eance's able article on the Surface- 

 geology of the Lake Districts, in which he repeatedly refers to an 

 article by me in your number for July, 1865, was written before 

 the publication of my work on the Scenery of England and Wales 

 (reviewed in your number for October last), in various parts of 

 which the Denudation of the Lake District is fully considered. In 

 reply to several of Mr. De Eance's observations, I would remark — 

 (1) that I don't regard the probable absence of erratic blocks on the 

 Pennine Hills at a greater height than 1800 feet above the sea as a 

 presumption that the Lake District was not submerged to a greater 

 depth than that implied by these erratics, because at a greater depth 

 the extent of coast-ice, or floating glacier-ice, capable of transportuag 

 blocks, must have been much reduced, owing to the decreased area of 

 land above water, and likewise perhaps owing to an amelioration of 

 climate, to say nothing of possible changes in the direction of cur- 

 rents. If I mistake not, erratics transported from short distances 

 have been found in the Lake District which must have been floated 

 over ridges rising to a greater height than 1800 feet above the pre- 

 sent sea-level. 



(2) Deflected or branching sea-currents, assisted by waves, may 

 have acted very powerfully on the western side of Thirlmere Valley 

 at the time when it was a strait ; and supposing the eastern side of 

 Helvellyn to have been once a longitudinally-strait slope, consisting 

 of rocks varying in structure and hardness, the sea undoubtedly 

 would have broken up this slope into coves and capes. "Were the 

 sea now to attack the eastern side of Helvellyn, it would probably 

 destroy the edges, and fill up the cwms, because the sea generally 



