Correspondence — Mr. Wm, Ilarte, 439 



We often find lignite in the state described in the indurated Car- 

 boniferous rocks themselves, and here we may get some little 

 inkling as to the nature of metamorphic action. 



We know that the basalt (4) was very hot ; that the lignite clay 

 (3) was hot too ; that the flint bed (2) was hot also ; and that the 

 limestone (1) was at least very warm. At the time of this basaltic 

 outburst the whole district affected by it must have had a very high 

 temperature indeed, and the lime was deposited in a pasty mass. 

 Now why the lignite was not altered it is not necessary to discuss 

 here. I think a satisfactory reason can be shown, but I will only 

 remark that volatilizing matter in a compressed bed of clay, and in 

 a '* platinum capsule," are two very different things ; but a strong 

 heat transmitted through the clay (but not sufficient to indurate it) 

 would be quite sufficient to indurate a paste of lime below it. I for 

 one do not believe in the necessity for very great heat in meta- 

 morphic action. It has been observed that many substances 

 (minerals) seem only to have to be brought into close contact, to be 

 changed, under pressure, from loose particles to solid rocks. 



In a rough way, we observe this, when we break up the rich lime- 

 stones of the Co. Cork for instance, for road metal, and leave them 

 for years subject to pressure (which is convertible into heat), and 

 when we afterwards break up the mass, we find we have to quarry 

 an exceedingly hard breccia or conglomerate, and can scarcely even 

 disturb it with a pickaxe ; but take the basalts or earthy rocks (of 

 which bed 3 in diagram is only the waste), and all we can do will 

 not make a compact mass of them. 



We have then ample reason for admitting that the transmitted 

 heat of the superincumbent mass could affect and indurate the lime 

 below, but we must guard cautiously against the idea that the altera- 

 tion, or induration, or metamorphism of rocks, can only be affected 

 by a fierce heat. It remains yet to be shown that the basalt and the 

 induration of the white limestone " are not connected in the way of 

 cause and effect." 



Looking forward with much pleasure and confidence to the labours 

 of Professor Jukes in this new field in Ireland. — I am, &c., 



William Harte, C.E., 



County Surveyor of Donegal. 



County Surveyor s Office, Buncrana, Co. Donegal, 

 lOth August, 1868. 



:m:isc:hix.IjJL3^:botjs. 



Dr. Falconer on the Himalayahs.^— '^ The rock formations of the 

 Himalayahs are all primary; the Sub-Himalayan is very recent. 



1 Extract from a letter written by the late Dr. Hugh Falconer, in 1834, to the 

 Rev. Dr. Gordon, of Birnie, N.B., soon after his return from ascending the 

 Jumnootree as far as the hot springs at the sources of the Jumna. See Biographical 

 Sketch, p. xxxi., Falconer's Palseontological Memoirs, vol. i. ; reviewed in the present 

 No. of this Magazine, p. 423. 



