2S2 REPORT OF NATIONAL MUSEUM, 1904. 



In Emmons's work the minerals were all included in four classes, 

 with an appendix which contained those minerals of which but little 

 is known. The classes were subdivided, as Cleaveland and others had 

 done before him, into orders, the orders again into genera, and the 

 genera finally into species. His arrangement of classes was. how- 

 ever, somewhat different from any of his predecessors. Thus, the 

 first class included those minerals, not metallic, which are oxidable or 

 which are compounds whose bases are oxidable. It comprised native 

 gases and liquids, sulphur and carbon, and the carbon compounds, 

 but, singularly enough, no mention was made of graphite. 



The second class included all minerals which are metallic or whoso 

 bases are metallic; the third class all those which consist of an 

 alkaline or earthy base in combination with acids, and the fourth 

 those which consist of an earth or are compounds of earths with 

 variable portions of alkaline and metallic oxides. In the seven sec- 

 tions into which this last class was divided he placed quartz in all its 

 varieties, siliceous slate, pumice, obsidian, clinkstone, a large number 

 of hydrous and anhydrous silicates, argillite, wacke, clay, phosphates, 

 etc. But little attention was given to crystallography, and "silex, 

 alumnie, and lime are considered as the oldest of the earths, as they 

 (Miter into the composition of the primitive rocks.' 1 Altogether 297 

 species were recognized, 44 of which were mentioned in the appendix 

 as little known. Many of these, such as pumice, obsidian, wacke, 

 etc., can not, of course, be properly considered as minerals. In spite 

 of this unintentional exaggeration, it is interesting, for purposes of 

 comparison, to note that in the latest edition of Dana's Mineralogy 

 (1892) 824 species were recognized. 



The part of Emmons's work devoted to geology was made up mainly 

 of a ''general description of North American rocks." The classifica- 

 tion adopted was the same as that used by Eaton and need not be noted 

 here further than to say that he included an argillite among his primi- 

 tive as well as transition rocks, while Eaton limited argillite to the tran- 

 sition series, though recognizing the possibility of a primitive form. 



Among the early workers in stratigraphic geology, along lines laid 

 down by Cuvier, Brongniart, and their successors, mention must be 

 made of Gerard Troost, born in Holland in 1776 and dying in Nash- 

 ville, Tennessee, in 1850. Like man}' naturalists of 

 wo?k! ?826 His hi * time Troost was a physician. He studied in France ; 



was appointed by the King of Holland to accompany, 

 in a scientific capacity, a naval expedition to Japan. He was captured 

 and imprisoned by English privateers, finally returning to Paris. He 

 thence took passage for New York in an American vessel and was again 

 captured, this time by a French privateer, and once more imprisoned. 

 On his release he went again to Paris, was again allowed to embark, 

 and in 1810 came to Philadelphia. 



