David Forbes — Beply to Dr. T. Sterry Hunt, 107 



earthy oxidised matters, when by far the greater part of the globe 

 was probably solidified. Hence we now find them in the earth's 

 superficial crust." And a little further, "We cannot conceive any- 

 thing else than the production of a homogeneous oxydized silicated 

 mass, upon which, at a late period, would be precipitated the noble 

 metals." 



Chemists will not require any comments upon the above, for they 

 are accustomed to regard Platinum, for example, as one of the most 

 refractory bodies known, which, of course, cannot be the case now 

 that Dr. Hunt has made this interesting discovery of its great vola- 

 tility at a point at which silicates solidify ; and further, they were not 

 aware that the extreme refractory nature of the other metallic oxides 

 had been so completely demonstrated, since some of them, at least, 

 as Lead, Bismuth, Antimony, Molybdenum, etc., are not remarkable 

 for that property ; whilst geologists will not feel convinced from Dr. 

 Hunt's mere assertion that the noble metals have from the beginning 

 been in the earth's superficial crust, precipitated on to it from the 

 skies like Jupiter's golden rain, but may also be inclined to believe 

 that they may have been carried up from below. 



The only important point which Dr. Hunt now advances is 

 the courteous request for Mr. Forbes to explain "the intervention 

 of water in all igneous rocks, which, as he declares, are outbursts 

 from the still fluid interior of our globe." The above words do not 

 exactly express my views, since I advance that igneous rocks have 

 their sources in some ^'reservoir or reservoirs'" of still fluid matter in 

 the interior of the earth ; and I would add that, by the actions of 

 capillarity and heat, I see no difficulty in explaining the infiltration 

 of the requisite amount of water for the supply of such a source. 

 As, however, I could not even think of accusing Dr. Hunt of " un- 

 familiarity with geological literature," to use his own words, I 

 could not suppose him ignorant of the writings of Daubree, who, 

 in Europe, at least, is regarded as somewhat of an authority on 

 these subjects ; Dr. Hunt will find this question fully answered 

 by that gentleman, whose words are : " En resume, sans exclure 

 I'eau originaire, et en quelque sorte de constitution initiale, que Ton 

 suppose generalement incorporee aux masses interieures et fondues, 

 M. Daubree est porte a conclure de I'experience ci-dessus relatee, que 

 I'eau de la surface pourrait, sous Taction combinee de la capillarite 

 et de la chaleur, descendre j usque dans les parties profondes du 

 globe." 



Always preferring, when possible, a reference to fact or experi- 

 ment than to authority, 1 would advise Dr. Hunt, in order to form a 

 conception of such strange action, to examine a common Gifford or 

 other injector used to supply feed- water to a high pressure boiler, 

 and he will soon perceive that the very forces which otherwise would 

 prevent the entrance of the water into the boiler are the very means 

 of forcing it in. 



Dr. Hunt also asks me to remember " that the oldest known series 

 of rocks, the Laurentian, consists of quartzites, limestones, and gneiss 

 evidently of sedimentary origin and derived from still older sedimen- 



