THE CLASSIFICATION OF IGNEOUS ROCKS. 487 



the number of mineral constituents regarded as essential ; 

 thus there are unitary, binary, and ternary rocks.] 



(8) VOGELSANG, H. Ueber die Systematik der Gesteinslehre und 



die Eintheilung der gemengten Silikatgesteine. Zcits. Dents. 

 Geo/. Ges., vol. xxiv., pp. 507-544, 1872. [The primary 

 division into six "types" is based on the constituent 

 minerals, which are distinguished as of four ranks of dif- 

 ferent importance; subdivisions are based on structure, and 

 especially on the absence or presence of the porphyritic 

 character. While showing in his preliminary remarks that 

 the distinction of older and younger is logically untenable, 

 the author retains it in his tabular scheme.] 



(9) LASAULX, A. VON. Grundziige einer neuen Systematik der 



Gesteine. 8vo, 11 pp. Bonn, 1872. [Founded on (i.) struc- 

 tural and (ii.) mineralogical characters. Under the composite 

 crystalline rocks the main division is between porphyritic 

 and non-porphyritic. A brief review of the subject is pre- 

 fixed to the table." 



(10) CREDNER, Herm. Forsckldge su ehier neuen Classification 



der Gesteine. 8vo, 12 pp. Leipzig, 1873. [With several 

 departures from the Naumann-Zirkel arrangement adopted 

 in the author's Elemente der Geologic The age-criterion is 

 here abandoned.] 



(11) SZABO, JOSEF. Trachyte eingetheilt ' nach dem natiirlichen 



System. 8vo, 9 pp. Vienna, 1873. [An example of a 

 mineralogical grouping applied to the Tertiary lavas, the 

 author's "trachyte" including all these with the exception 

 of the olivine-bearing types. They are divided into "quartz- 

 trachytes " and " trachytes," and in each division are eight 

 groups based on the dominant species of felspar.] 



(12) Lasaulx, A. VON. Elemente der Petrographie. 8vo. Bonn, 



1875. [An example of a classification grounded on struc- 

 tural and textural characters.] 



(13) ROSENBUSCH, H. MikroskopiscJic PhysiograpJiie der Massigen 



Gesteine. 8vo. Stuttgart, 1877. [The main divisions are 

 based on the predominance of orthoclase, plagioclase. 

 nepheline, and leucite respectively ; the subdivisions on the 

 association with these minerals of mica, augite, hornblende, 

 and enstatite. The peridotite group is here first intro- 

 duced.] 



(14) Dana, J. D. On some points in Lithology. Amcr. Journ. 



Sci. (3), vol. xvi., pp. n6, 431, 1878. Partly reproduced in 

 Geol. Mag., pp. 222-225, 1879, with a criticism by T. G. 

 Bonney, pp. 199-203. [A loose mineralogical scheme in 

 which the genetic principle is wholly set aside.] 



