332 Correspondence — R. Mallet — M. Hall. 



COiai^IESIPOIsriDIED^GIE. 



NATUEE OF VOLCANIC HEAT. 



Sir, — ^In reference to Mr. Scrope's letter in the GtEOLOGical 

 Magazine for May, 1874, p. 237, I must exonerate myself from 

 ttiat gentleman's charge of " persistently continuing to saddle him 

 ■with the advocacy of one or both theories as to the origin of volcanic 

 heat, viz, a liquid nucleus and thin crust, or Hopkins's fiery lakes." 



An author's notions are usually gathered from his acknowledged 

 systematic works, and not from scattered magazine articles. I 

 am much mistaken if Mr. Scrope has not throughout his systematic 

 •works adopted one or both of the above theories. On reference to 

 the articles in your Magazine from Mr. Scrope's pen, referred to by 

 you in your foot-note (Geological Magazine, March, 1874, p. 127), 

 as modifying or repudiating the above theories, I am compelled to 

 repeat what I have already stated in your April Number, that 

 nothing contained in them appears to me to justify the statement 

 made by you that I " misapprehended," ^ and now by Mr. Scrope him- 

 self, that I have misrepresented him. 



Whether Mr. Scrope's subterraneous reservoirs be left as unex- 

 plained as to their origin, as Hopkins left his lakes, or be assumed to 

 be derived from a rise in geothermal temperature produced by deposi- 

 tion of sediment, makes no difference as respects the validity of the 

 objections which I have urged as equally applicable to both. No body 

 can raise the temperature of another by conductive transference of part 

 of its heat to a temperature as high as its own. If, therefore, the sub- 

 cortical matter of our globe, as Mr. Scrope terms it, " passes locally 

 under varying conditions of heat and pressure '"'^ ► . . "to a 

 liquid or even vaporous state," there must be matter more deeply 

 situated at a still higher temperature, i.e. there must be a liquid 

 nucleus. Things as essentially different and distinct as are the views 

 which I have enunciated as to the nature and origin of volcanic heat 

 and energy from those anywhere enunciated by Mr. Scrope, may 

 easily be made obscure or confused by fragmentary controversy. I 

 must therefore decline to go further in this direction. I have re- 

 duced my own views as to the nature and origin of volcanic heat to 

 the brief and unmistakable form of a definition (Phil. Trans. 1873, 

 vol. i. para. 67, p. 167). Every clear-cut thought and theory can be 

 reduced to the same form. That neither I nor your readers may 

 mistake further (if I have already done sa at all) Mr. Scrope's 

 views, will he be good enough to reduce them to a definition? 

 Definitions do not involve any dogmatism,^ and are extremely 

 serviceable in preventing misconceptions, whether arising from 

 obscurity of expression or of thought. 



Ibth May, 1874. KoBEKT MalleT. 



A PEOPOSAL FOE A SWISS GEOLOGICAL EAMBLE. 

 Sib, — I beg leave to draw the attention of the readers of the 

 G-EOLOGiCAL Magazine to a proposed Swiss tour, which might be a 



1 We are content to refer the impartial reader to tlie articles iu question and to 

 Mr. Poulett-Scrope's published works. — Edit. Geol. Mag. 



