ANNIVERSARY ADDRESS OF THE PRESIDENT. Ixxix 



their association was, that these latter had also been formed by the 

 sublimation and subsequent oxidation of chlorine combinations. It 

 is, perhaps, still doubtful whether we may conclude, with the emi- 

 nent Berlin Professor, that this discovery rehabilitates the sugges- 

 tion of Scacchi, who ascribed, years ago, the fine crystallization of 

 numerous silicates of the A^csuvian lavas, such as melanite, sodalite, 

 hornblende, felspar, &c., to sublimation. 



Subterranean Temperature. — In connexion with the change of 

 rock masses by metamorphic action, and with the phenomena of vol- 

 canic forces, we are constantly reminded of the internal tempera- 

 ture of the globe, and find it difiicult to establish any clear view 

 of the causation of either one or the other without being first satis- 

 fied of the reality and amount of this internal heat. Confessedly 

 there are many difiiculties in the way of a sufiicient knowledge of 

 the character of the interior of thp earth, even to a moderate depth ; 

 but surely among the main facts upon which we may depend is 

 that of an increase of temperature with increasing depth. Such is, 

 however, the desire on the part of certain writers to launch their 

 own novelties and to upset the old landmarks, that one has seen 

 this position of late altogether questioned, or an explanation of the 

 increased heat proposed in the compression of the air, the friction 

 caused by the working of mines, and in the warmth of men, the 

 burning of candles, gunpowder, &c. All these are doubtless efficient 

 causes, and in inquiries pretending to accuracy must be either 

 avoided or eliminated ; but they have long since been shown to be 

 inadequate to produce the results obtained*. 



Although, as I believe, all actual observers are agreed upon the 

 main point at issue, it is very true that a great uncertainty pre- 

 vails as to the rate of elevation of temperature met with in descend- 

 ing, whether it be according to a regular scale of progression, 

 increasing directly with the depth, or be intermittent, as main- 

 tained long ago by Mr. E. W. Tox — whether it increases below a 

 certain horizon in a less rapid ratio, and, after reaching a given depth, 

 again more rapidly — and how much it may vary in the difi'erent 

 classes of material which make up the crust of the earth. These 

 data we doubtless ought to be able to obtain from multiplied care- 

 ful observations ; but the more remote question, viz. the cause of 

 such increase, is far more difficult of solution, and yet need not 

 perhaps for ever baffle the inquiries of man. A further and grow- 

 ing reason for inquiry into this subject exists in its bearing upon 

 deep-mining operations; and through some of these, completed of 

 late years, we obtain valuable confirmation of the principal facts 

 on which most geologists have long been inclined to rely. 



Among accurate researches into the temperature of the earth at 

 great depths, those of M. Walferdin (published in the Comptes 

 Rendus) are well deserving of attention, carried out as they were 

 in a bore-hole deeper than any which had previously been executed. 

 The massive and yet contorted principal seam of coal at Creuzot 



* See the masterly essay of Cordier, ia the M6in. de I'lnstitut, torn, vii., and 

 the papers of E. W. Fox, F.R.S. 



