OHAPTEE V. 
PETROGRAPHICAL DESCRIPTION OF THE BASIC ERUPTIVES. 
NOMENCLATURE. 
Many of the petrographical data upon which uniformitarian argu- 
ments have been based have been drawn from the comparative study 
of basic eruptives, and there is a marked disposition to disregard age 
in the nomenclature of these rocks. Among German petrographers, 
Keyer, 1 Tietze, 2 Eeiser, 3 Eeusch (H. H.), 4 and Sness r ° have supported the 
view that age is not a just ground of distinction between eruptive 
rocks, and Rosenbusch 6 predicts that in no very distant future the 
separation of effusive rocks into an older and a younger series "will 
prove untenable." English and American petrographers are practi- 
cally disregarding age m their nomenclature of the basic igneous 
rocks. Among the former, Judd, T Teall, 3 Allport, 9 Bonney, 10 Phillips," 
and Hobson 12 are notable. Among American petrographers, the 
Danas 13 and Iddings 14 have disregarded age in their usage of basic 
rock names. 
In plagioclase-augite rocks, the distinction between the gabbro and 
the diabase groups has been finally recognized as structural and 
not inineralogical, and the distinction between the diabase and the 
>E. Reyer, Beitriige zurFisikderErup., 1877, pp. 142-171 ; ref. Hussak : Neues Jahrbuch fur Minei al., 
etc., 1892, Vol. II, p. 147. Beitrage zurFisik der Erup. und der Eruptivgesteine 1887, p. 135. 
2 E. Tietze, Das Altersprincip bei der Nomenclatur der Eruptivgesteiue: Verhandl. k. k. geol. 
Eeichsanstalt, Wien, 1888, p. 166; ref. E. Becke: Neues Jalirbueh fur Mineral.. Vol. II, 1884, p. 303. 
3 Karl A. Eeiser, Ueber die Eruptivgesteine des Algaii: Tschermaks mineral. Mittheil., Vol. X, 
1889, pp. 500-550. 
4 H. H. Reuscb, Ueber Vulkanismus, Berlin, 1883, 
c Suess, Das Antlitz der Erde, Vol. I, pp. 204-206, 1883. 
6 H. Eosenbuscb, Ueber die ckemischo Beziebungen der Eruptivgesteine: Tscherniaks mineral. 
Mittheil., Vol. XI. 1890, p. 146. 
' Judd, On the gabbros, dolerites, and basalts of Tertiary age in Scotland and Ireland : Quart. Jour. 
Geol. Soc. London, Vol. XLII, 1886, pp. 49-97. The secondary rocks of Scotland: Quart. Jour. Geol. 
Soc. London, Vol. XXX, 1874, pp. 220-303. 
»Teall, Address of the president Geol. Sec. (e) of the British Assn. Adv. Sci., 1893. 
9 Allport, On the basaltic rocks of the Midland coal fields: Geol. Mag., Vol. VII, No. 70, 1870, pp. 
159-162 Tertiary and Palaeozoic trap rocks: Geol. Mag. Vol. X, 1873, p. 196. 
)0 Bonney, Quart. Jour. Geol. Soc. London, Vol. XXX, p. 529. 
"Phillips, On the so-called greenstones of central and eastern Cornwall: Quart. Jour. Geol. Soc, 
London, Vol. XXXIV, p. 471. 
12 Hobson, On the basalts and andesites of Devonshire : Quart. Jour. Geol. Soc, London, Vol. XL VIII, 
1892, pp. 496-507. 
13 J. D. Dana, On some points in lithology: Am. Jour. Sci., 3d series, Vol. XXXVIII, 1878, pp. 
336, 438. E. S. Dana, Trap rocks of the Connecticut Valley: Proc Am. Assn. Adv. Sci., 1884. 
14 Iddings, The columnar structure in the igneous rock on Orange Mountain, New Jersey: A.m. 
Jour. Sci., 3d series, Vol. XXXI, Mav, 1886, p. 331. 
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