R^SUM^, AND GENERAL DISCUSSION. 525 



In view of the contradictions and confusion of ideas thus shown to 

 prevail among the most eminent geologists in reference to the uonieu- 

 clature of the oldest crystalline rocks, no one can do otherwise than 

 admit that it is quite time that some more definite understanding 

 should be had of this whole subject, and, as a contribution toward this 

 desirable end the following remarks are submitted. 



There are two essentially different ways of looking at the rocks which 

 make up that portion of the earth which is accessible to investigation. 

 One of these has reference to the manner in which these rocks have 

 been formed ; the otlier, to the chronological order in which they have 

 come to occupy the position which they now hold. Roughly speaking, 

 it is this idea which forms the basis of a division of the science of ge- 

 ology into two quite distinct departments, Dynamical and Historical 

 Geology. For the study of the former a knowledge of lithology and 

 petrology is indispensable, while the latter is chiefly an application • of 

 the results of palccontological investigation to questions of synchronism 

 and order of succession in the rocky strata. 



In considering other worlds than our own, no more important ques- 

 tion could be asked in regard to them than this : Are they inhabited, 

 or does organic life exist upon them] The only reason why this ques- 

 tion is not oftener asked or more discussed is, that it is one to which a 

 definite answer cannot now be given, while there seems to be extremely 

 little chance that there will ever be any change in this respect. It is 

 not beyond the bounds of possibility that some meteoric fragment may 

 be dropped upon this earth bearing evidences of the existence of life on 

 another world ; but, up to the present time, the aspect of such bodies 

 as have come to us from outside our own atmosphere has not been 

 of a character to encourage any expectation that such an event may 

 occur in the future. Still, it will hardly be denied by any one that 

 proof of the existence of life on any of the planets, or any other of the 

 heavenly bodies, would be accounted one of the most interesting revela- 

 tions ever made to the human race. Similarly, to fix in the order of 

 events through which this earth has passed the epoch when life began 

 to exist on the globe, must be admitted to be a problem of high impor- 

 tance ; and, as intimately connected with this, and of similar interest, 

 would necessarily be the inquiry whether any rocks could be pointed 

 out in regard to which it could be affirmed with truth that they were 

 deposited, or brought iuto their present position, before the appearance 

 of life on the earth. 



Here, however, a point suggests itself as of importance in connection 



