PREHISTORICAL VIEWS 6 



ble that the philosophers of these earlier civilizations may have indulged 

 in speculations as to the origin of the metals, but if so they left no writ- 

 ten record. Even among the Romans, of whose proficiency in mining 

 evidence is found in most of the mining regions that came under their 

 control, little or no genetic speculation was indulged in,- if we accept 

 the evidence of Pliny's " Natural History." This monumental work, 

 which is assumed to contain a complete and faithful presentation of 

 the knowledge of natural phenomena at the opening of the Christian 

 era, though it described in considerable detail the methods of mining 

 then in vogue, does not even attempt a description of the mode of occur- 

 rence of the ores, much less speculate on their origin. 



The historic time here contemplated may be divided in a general way 

 into three periods, according to the prevailing method by which the 

 views then current were arrived at : 



Development of Knowledge historically considered 



the three periods 



1. The speculative period, in which, from a few rather imperfectly de- 

 termined facts of nature, general theories were evolved intended to be 

 applicable to all natural phenomena. It was a period in w r hich geology 

 was not yet recognized as a distinct science and had hardly reached the 

 dignity of an adjunct to mineralogy. 



2. The second period was that in which facts of observation had ac- 

 cumulated sufficiently to establish geology on the basis of a distinct 

 science, but in which the method of reasoning from generals to particulars 

 still prevailed. This was the first scientific period. 



3. The third period might be called the period of verification, in which 

 the theories already propounded were tested by experiment or observation. 



Such a classification is in the nature of things not susceptible of a very 

 definite demarcation, either in point of time or in the assignment to either 

 period of individual opinions or theories, but the attempt to make it, 

 however imperfect and unsuccessful it may prove, will assist us to form 

 a clearer conception of the progress of human thought and of the methods 

 by which it has arrived at its present understanding of the particular 

 branch of geological science which we are considering. 



THE SPECULATIVE PERIOD 



During the first, or speculative period, which may be assumed to have 

 extended up to the close of the eighteenth century, or to the time of 

 Werner and Hutton, the accumulation of accurately determined facts 



