4 S. F. EMMONS — THEOKIES OF ORE DEPOSITION 



that would bear on the theory of ore deposits was so extremely limited 

 that it may be assumed to have exercised but little influence on the 

 development of the science beyond the suggestion it afforded to later 

 students of lines of investigation to be followed, and hence may be passed 

 over in a very cursory manner. 



In the speculations of this period, which especially influenced the 

 development of opinion, two general types may be distinguished : 



First, the broader theories of the Cosmic philosophers with regard to 

 the formation of the earth based more or less upon astronomic data; 



Second, the special theories of mineral vein formation conceived by 

 individuals and based in the main on general conceptions which were sup- 

 plemented by a certain amount of personal observation and experience. 



The Cosmic philosophers were men who, without being geologists in 

 the modern sense of the word, nevertheless put forth ideas with regard 

 to the system of the earth that had an undoubted influence on the minds 

 of those who have since made a special study of this part of science. 



First of these was Descartes, the French mathematician and founder 

 of the Cartesian system of philosophy ( u Principia," 1644), who consid- 

 ered the earth a planet like the sun, but which, though cooled and con- 

 solidated at its surface, still preserved in its interior a central fire that 

 caused the return toward the surface of waters of infiltration, the filling 

 of veins by the metals, and the dislocations of the solid crust. 



Nearly contemporary with him was Steno, a Danish physician, who 

 spent the greater part of his life in Italy, where he devoted much of his 

 time to the study of geological phenomena. He was the first to seek to 

 learn the origin of rocks and the changes in the earth's crust by the in- 

 ductive method. He wrote a remarkable treatise, bearing the quaint 

 title " De Solido intra Solidum naturaliter Contento " (1669), in which he 

 considers vein fissures to be later than the enclosing rocks, and their 

 filling to result from the condensation of vapors proceeding from the 

 interior. Steno's ideas, so much in advance of those of his age, seem to 

 have found little favor among his contemporaries, and were scarcely 

 known among geologists, until called to their attention in the first half 

 of the nineteenth century by de Beaumcnt and von Humboldt. 



Later, Leibnitz, a German philosopher, inspired both by the ideas of 

 Descartes and the observations and deductions of Steno, wrote a work 

 on the origin of the earth (" Protogsea,' 1 1691), which, 'in spite of its neces- 

 sarily limited basis of facts, bears the imprint of genius in its conceptions. 

 In applying his theories to the veins of the Hartz, which he had occasion 

 to visit during his thirty years' sojourn at Hanover, Leibnitz considers 

 that they have been filled sometimes by the liquefying action of fire, 

 sometimes by water. 



