THE SPECULATIVE PERIOD 5 



In the following century, Buffon, the great French philosopher, excited 

 to the highest degree the attention of the scientific world by his "Theorie 

 de la Terre " (1749) and " Epoques de la nature " (1778). His concep- 

 tions, 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 opened in the mountains 

 through the force of contraction, and that they were filled by metals 

 which, by long and constant heat, had separated from other vitrifiable 

 materials. But as there are non-vitrifiable as well as vitrifiable materials 

 in veins, so there are secondary veins which have been filled with non- 

 vitrifiable minerals by the action of water. The primary veins he con- 

 siders to be characteristic of high mountains, while the secondary veins 

 occur rather at the foot of the mountains, and probably derived some of 

 their material from the primary veins. 



In the second class the foremost place, both in time and in the impor- 

 tance of his actual observations, must be accorded to Dr George Bauer, 

 better known by his latinized name of Agricola, a German physician, 

 who flourished during the first half of the sixteenth century. He spent 

 a great part of his life among the mines of Saxony (Joachimsthal), of 

 which he made a careful study. He wrote, in most excellent latin, several 

 works on mineralogy and on the art of mining, which were for centuries 

 standard books of reference on these subjects, and even to the present 

 day contain much of interest to the mining engineer. Agricola was first 

 and foremost a mineralogist, and all his work was characterized by acute- 

 ness of observation and accuracy of description, though, in strong con- 

 trast to most of the early writers, he did not indulge much in earth-for- 

 mation theories. He divided mineral veins into u commissural " (joints 

 or rents), " fibrse " (small branching veins), " vense " (large veins or chan- 

 nels), and " terrse canales " (vein systems), and gives a clear account of 

 their size, position, intersections, etcetera. In theoretical matters he was 

 less definite and satisfactory. 



During all this period the two main subjects of speculation with regard 

 to mineral veins, which term practically included all ore deposits, were 

 (1) their age relative to the rocks in which they are found, and (2) the 

 cause and manner of their filling ; and in considering the views put for- 

 ward on these subjects, we must bear in mind that chemistry as a science 

 only came into existence toward the end of the eighteenth century ; hence 

 the ideas which were entertained as to the processes that may have gone 

 on within the earth's crust to form metallic deposits were necessarily 

 somewhat vague and fanciful. 



