﻿ANNIYEESAHX ADDBESS Or THE PRESIDENT. lv 



Professor Naumann in his ' Lehrbuch der Geognosie,' the most 

 copious and instructive general treatise on geology with which I am 

 acquainted, briefly notices the conjectures of other geologists as to the 

 agencies in normal or general metamorphism, without expressing any 

 decided views of his own, except as to what heat may be supposed to 

 have effected. But he enters at considerable length into the subject 

 of abnormal or local metamorphism. He justly observes that while 

 here the origin of the effect is apparent, the modus operandi is far 

 from being equally so in a great proportion of cases. In the generality 

 of instances the heated state of the intrusive rock appears to have been 

 the cause ; but he adds, " it is nevertheless evident that many of the 

 appearances when ordinary sandstones and quartzose conglomerates 

 are changed into quartzite by the contact of granite, syenite, and 

 other pyrogenous rocks cannot be explained by the action of heat 

 alone. For it is difficult to conceive that heat, which in its con- 

 tinuous state, at least, could not have been very great, and must at 

 all events be much under the melting-point of silica, could convert 

 a fragmentaiy sandstone into crystalline quartzite. It is clear that 

 such eontact-metamorphism must belong to those instances the 

 production of which without the concomitant action of water is in- 

 conceivable*." 



There is an observation of M. Daubree, which, so far as I know, is 

 novel and is well deserving of being followed up in researches in 

 metamorphism. He states that cases of the metamorphism of 

 sedimentary rocks occur only in those situations where disturbances 

 of the horizontality of such deposits have taken place : that the oldest 

 strata of Russia, Southern Sweden, and North America have preserved 

 their original horizontality and are not sensibly metamorphosed. 

 That, on the other hand, newer strata which have been much broken 

 up and elevated, such as the jurassic and cretaceous formations of the 

 High Alps, the Apuan and the Tuscan Alps, have been completely 

 modified, few only of the eruptive rocks being met with among them : 

 that clay-slates are but the beginning of more deeply-seated trans- 

 formations, and occur only in regions more or less disturbed : that 

 hot springs are always connected with accidents in the structure of 

 a country of a similar kind : that it is therefore difficult not to per- 

 ceive a connexion between the two phenomena, and no less difficult 

 to refuse one's assent when we learn by experiment that the mineral- 

 ized waters are among the most energetic agents in that metamor- 

 phism which we can artificially produce f. 



Gneiss is generally held to be a metamorphic rock, meaning thereby 

 that it was originally a sedimentary deposit of the detritus of a pre- 

 existent surface-rock, altered by subterranean heat as the chief 

 agent. There are, however, some considerations which make it 

 difficult for me to understand the modus operandi of this supposed 

 thermal action ; that is, in what manner the heat could be applied, 

 in accordance with known chemical laws. If gneiss be, as it is 

 usually held to be, the lowest known of the sedimentary stratified 



* Lehrbuch der G-eognosie, i. 793. 

 t Observations, &c. p. 38. 



