SYSTEMATIC PETROGRAPHY 463 



to the strongly stated conclusion that " all the volcanic rocks 

 show abundant evidence of fusion in the presence of glass base 

 and glass inclusions, while the group which is typified by granite 

 never shows the slightest trace of the effects of fusion." All 

 known characters of plutonic rocks are interpreted as proving 

 them to be extreme products of the metamorphism of sediments. 

 After discussion of the cause of generic differences of volcanic 

 rocks, in which certain new hypotheses concerning magmatic 

 differentiation are developed, King proposes the following sys- 

 tematic arrangement for the family of volcanic rocks, including 

 therein all believed to be of truly igneous origin : 



Genera. — (r) Propylite ; (2) Andesite ; (3) Trachyte; (4) Neolite. 

 Expressions of time, according to von Richthofen's law of succession, and of 

 depth owing to secular refrigeration. 



Species. — Expressions of chemical differentiation by specific gravity of 

 mineral ingredients, grouping under the law of Bunsen. 



Three species only were recognized under each genus, repre- 

 senting respectively the quartz, biotite or hornblende, and 

 pyroxene-bearing forms. 



Varieties. — Expressions of range of texture according to predominance 

 of secreted crystals, groundmass, or base. 



M. E. Wadsworth, 1884. — Under the title Lithological Studies; 

 A Description and Classification of the Rocks of the Cordilleras, M. 

 E. Wadsworth published, in 1884, the first part of a projected 

 comprehensive work, intended to present a new classification of 

 rocks. This first part was devoted to a discussion of principles 

 and the beginning of the descriptive portion. Wadsworth 

 denounced all existing systems as highly artificial, and stated, as 

 the basis of his own more natural system, the belief that " the 

 older rocks now classed as distinct species are rocks that were 

 once identical with their younger prototypes." " The order [of 

 his system] will be to pass from the glassy to the most perfectly 

 crystalline state ; from the least altered to the most altered ; 

 from the most basic toward the most acidic ; from the non- 

 fragrrental to the fragmental or clastic." He plunged at once 

 into a description of ultrabasic rocks, without explaining the 



