304 EXPERIMENTS ON METAMORPHISM, ETC. 



contraction which afterwards produced mountain chains. This force 

 was perhaps limited in these first epochs to producing the schistose 

 character of the rocks, at the same time that, by reason of their flex- 

 ibility, it augmented their thickness by folding, while scarcely undu- 

 lating them. 



Whatever may be the fate of hypotheses by which we allow our- 

 selves to be carried away, even while recognizing that they rest as 

 yet on grounds not sufficiently solid, we have a right to believe that 

 the older gneiss demonstrates the high temperature of the globe in 

 very ancient times. The universal production of crystalline rocks in 

 these fundamental formations concurs with the whole assemblage of 

 metamorphic phenomena to compel the admission of a general cool- 

 ing of the interior of the globe. It is an argument of the most pos- 

 itive nature to oppose to the indiscriminate partisans of existing 

 causes, who, with Hutton, envelop the origin of our planet in a 

 night of indefinite duration, during which geological phenomena 

 never ceased to revolve in the same circle. 



Although these questions are still very obscure, we discover a grand 

 simplicity of agencies which have given rise to a great diversity of 

 effects; and the immediate productions of a superheated sea, the crys- 

 tallization of eruptive rocks, the metamorphism of stratified beds, 

 appear to be only difii"erent modes of action of the same phenomenon 

 in different ages. Conclusions less vague, however, should be ad- 

 journed to the time, perhaps not far distant, when we shall succeed 

 in producing granite artificially. Synthetical experiment has already, 

 since the time of Hall, been exceedingly useful, and it is to it that 

 the office of throwing still more decisive light on a formation where 

 direct observation has doubtless little more to learn, appears to be- 

 long. If experimentation, armed with its most ingenious processes, 

 has been necessary for understanding the phenomena which belong to 

 our own day, and of which we are witnesses at all times, such as the 

 weight of air, lightning, &c., with how much greater reason ought 

 we to have recourse to it when the question relates to geological facts, 

 the most important of 'which are not now repeated at least under our 

 observation, and have left as the only witness a final result, preserving 

 no trace of the intermediate activities which have produced it? 



Up to the end of the last century geology was altogether hypo- 

 thetical ; it then entered upon a positive career based upon the ob- 

 servation of facts and induction. It is not long since a new era seems to 

 have opened in which it seeks light from phenomena of every order — 

 chemical, physical, and mechanical — by synthetic experimentation, 

 thus undergoing the phases which physics have passed through 

 since the time of Galileo, to arrive at the point which it has now 

 attained. 



