312 THEOKIKS OF ORE DISPOSITION HISTORICALLY CONSIDERED. 



were .suppleniented by a certain amount of personal observation and 

 experience. 



The cosmic philosophers Avere men who, without l)eino- geologists in 

 the modern sense of the word, nevertheless put foi-th ideas witli re- 

 gard 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 (Principia, 1044), who 

 considered the earth a planet like the sun, but which, though cooled 

 and consolidated at its surface, still preserved in its interior a central 

 tire that caused the return toward the surface of waters of infiltra- 

 tion, the filling of veins by tlie 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 nnich 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 inductive method. He wrote a remarkable treatise, bearing 

 the quaint title '' De Solido intra Solidum naturaliter Contento " 

 (1069), in which he considers vein fissures to be later than the inclos- 

 ing 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 contempo- 

 raries, and were scarcely known among geologists until called to their 

 attention in the first half of the nineteenth century by de Beaumont 

 and von Humboldt. 



Later Leibuitz, 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 (Protogani, 1691), which, in spite of 

 its necessarily limited basis of facts, bears the imprint of genius in its 

 conceptions. In applying his theories to the veins of the Ilartz, 

 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. 



In the following century Buffon, the great French philosopher, 

 excited to the highest degree the attention of the scientific Avorld by 

 his Theorie de la Terre, 1749, and Fpoques de la Nature, 1778. His 

 conceptions, though striking by the brilliancy of their imagination, 

 have for the most part not proved of enduring value. Nevertheless 

 they served a purpose by stimulating more exact observations on the 

 points with regard to which his views were contested. With regard 

 to mineral veins he held that they were primarily fissures opi'ued 

 in the mountains through the force of contraction, and that they 

 were filled by metals which by long and constant heat had separated 



