SAS ALR CN TEE IAI BIG SOCIAL) a 355} 
proposition in classification which does not require full discussion 
in this place. Reference is had to Bunsen’s hypothesis of two 
fundamental magmas—the trachytic and the pyroxenic— mix- 
tures of which were supposed to produce all igneous rocks.’ 
From. the systematic standpoint Durocher’s hypothesis had the 
same result, though differing somewhat from Bunsen’s in the 
physical origin of the magmas. MDurocher (1857) carried out 
a chemical division of igneous rocks on his hypothesis, forming 
the acid, hybrid, and basic groups? Th. Kjerulf3 (1857) pro- 
posed four chemical groups: acid, neutral, basic, and ultra-basic, 
and various authors recognized the grand division of aczd and 
basic. Such divisions, when closely connected with hypotheses, 
have had more influence upon the geologist than upon the sys- 
tematic petrographer; for it was quickly found that, although 
the fundamental idea might be near the truth, the theory was too 
imperfect (or narrow) to explain the observed range in chemical 
composition of igneous magmas. The broad chemical distinc- 
tion, considered merely as a recognition of the observed range 
in composition of rocks, was not given sufficient precision to be 
of much value in system. 
Geological classifications—During these years of patient 
research, especially into the composition of igneous rocks, 
geologists were making important contributions to the broader 
phases of classification. As a knowledge of occurrence, rela- 
tion, and modes of formation of rocks increased many different 
factors were tested as to their applicability to the formation of 
systematic arrangements. Soon the numerous geological stand- 
points from which rocks might be viewed and classified led to a 
great many schemes for their arrangement, and much confusion 
existed. This condition continued until the geologist separated 
the systematic classification of rocks from various other arrange- 
™R. BUNSEN, “ Ueber die Processe der vulkanischen Gesteins-bildungen Islands,’’ 
Poggendorf’s Annalen, etc., Vol. LXX XIII, 1851, pp. 197-272. 
2J. DUROCHER, “Essai de pétrologie comparée,” etc., Annales des Mines (5) Vol. 
MEETS 7p. 27. 
3 Nyt magazin for naturvidenskaberne, Vol. IX, 1857, p. 294. 
