22 DE. THOMAS STEEET HUNT ON THE 



rocks ; a hypothesis of their origin which may be aj^propriately designated as thermo- 

 chaotic. According to this hypothesis, as set forth by Scrope, and afterwards by Delabeche 

 and by Daubrée, the first water on the surface of the planet would be condensed under a 

 pressure equal to 250 atmospheres, corresponding to a temperature near that of redness. 

 We are reminded in this of Dana's earlier metamorf)hic theory, in which he also invoked 

 the action of waters at a red heat. These, however, were supposed by him to be heated 

 in the depths of the ocean by local volcanic eruptions, and the process, so far from being 

 a universal one belonging to a very early time in the history of our planet, was a partial 

 one repeated at dittereut geological periods. 



According to Daubrée the original plutonic rocks are not known, and the oldest 

 crystalline schists are thermochaotic. Macfarlane, on the contrary, while adopting this 

 hypothesis for the later crystalline or transition schists, maintains the endoplutouic origin 

 of the primitive gneisses. 



§ 42. Proceeding now to review briefly the claims of the above hypotheses, we remark 

 with regard to the first, that multiplied observations in many parts of the world have now 

 established the existence of a regular succession in the crystalline rocks, which show by 

 the greater corrugation of the lower members, by frequent discordances in stratification, 

 and by the presence of fragments of the lower in the higher strata, that the order of 

 generation was from below upwards. With this, moreover, corresponds the fact that the 

 lower rocks are the more massive and more highly crystalline, while the upper ones pre- 

 sent a gradual appi'oximation in physical characters to the uncrystalline sedimentary or 

 secondary strata ; thus justifying the name of transition, applied by Werner to these inter- 

 mediate rocks. All these facts are irreconcilable with the endoplutouic hypothesis. 



The universal distribution, and the persistency of characters of these various groups 

 of crystalline rocks, indicate moreover that they have been produced by a world-wide 

 action, extending with great regularity through A'ast periods of time, and are incompatible 

 with anything which we know of the phenomena of vulcauicity. The objections long 

 since made by Naumaun to the second or exoplutonic hypothesis are still as valid as ever, 

 and there is no evidence in the lithological characters of these rocks of their volcanic 

 origin. The argument derived from the similarity between their mineralogical composition 

 and that of erupted rocks, of paleozoic and more recent times, is equally strong in favor 

 of the derivation of these latter from the primitive strata. 



§ 43. The metamorphic hypothesis, which would derive the primitive strata from the 

 consolidation and the recrystallization of detrital plutonic rocks, whether endoplutouic or 

 volcanic, is, for many reasons, inadmissible. Without at present considering the later crys- 

 talline groups, which are also of vast extent, the ancient granitoid gneisses, (originally 

 called Laiirentian and represented in Canada by the Ottawa and Grreuville series,) have an 

 unknown volume, since their base has neA'er been detected. It is, however, certain that 

 they include, wherever studied in Europe or in America, a vast thickness which, as Dana 

 correctly says, cannot be assumed to be less than 30,000 feet. The detrital hypothesis 

 demands an agency which shall create, transport, and lay down beneath the sea, over vast 

 areas, now continental, this enormous thickness of sediment, not of mingled sands and 

 clays, like those of later deposits, (which are the results of a more or less complete sub- 

 aerial chemical decomposition of primitive rocks,) but in a chemically unchanged condition, 

 and with the feldspar unaltered. It, moreover, demands a source for these enormoiis 



