310 THEOKIES OP ORE DISPOSITION HISTORICALLY CONSIDERED, 



necessary to state, only to the processes involved in the formation 

 of dei^osits that form an integral part of the rock in which they 

 occur, or " rock in place," as is the legal phraseology of the day, and 

 does not include such recent detrital deposits as placers, etc., aljont 

 whose origin there has never been any wide divergence of opinion. 



PREHISTORICAL VIEWS. 



The historic period is assumed to have been entered on only with 

 the revival of learning about the time of the Iveformation at the 

 connnencement of the sixteenth century. What few records can be 

 found of genetic opinions held before that time, even as to the more 

 striking and readily observable geological phenomena, such as vol- 

 canic eruptions, earthquakes, and changes in the earth's surface, are 

 too scattered and fragmentary to afford evidence of any continuous 

 development of thought. The views of the Pythagorean and Aris- 

 totelian schools of philosophy on the causes of these natural phe- 

 nomena, though apparently based more on bold poetical fantasy than 

 exact observation, present a clearer and more logical conception than 

 that which obtained nearly twenty centuries later. Thus it is said 

 that as early as COO B. C. the observed occurrence in the rocks of 

 casts of shells and plants were ascribed to periodical floodings of 

 the land. During the Middle Ages, however, under the monkish 

 influence that discouraged any views that might tlirow doubt on the 

 literal correctness of the Mosaic cosmogony, these fossils were vari- 

 ously assumed to have been formed in place l)y the agencies of the 

 stars, to have been transformed from rock hy some plastic force 

 (vis plastica), or left by the waters of the Noachian deluge. 



Among the early cosmogonies, which it is true are of mythologic 

 rather than of scientific interest, the Chinese is the only one which 

 included metal among the elements of creation. Yet the general use 

 of the metals, whose extraction from their native ores presup])Oses 

 a knowledge of the art of smelting^in itself an evidence of a certain 

 insight into nature's processes — goes back to very remote antiquity. 

 It seems possible 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 written 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 Ave accept the evidence of Pliny's Natural His- 

 tory. This moiuunental work, which is assumed to contain a com- 

 plete and faithful presentation of the knowledge of natural phe- 

 nomena at the opening of the Christian era. though it described in 

 considerable detail the methods of mining then in vogue, does not 



