378 HENRY S. WASHINGTON 
given below demonstrate how, of two magmas of practically identical 
chemical composition, the one which solidifies under intrusive con- 
ditions will be free from leucite, the potash going only into orthoclase 
in conformity with the norm, while in effusive flows leucite is apt to 
be formed, the amount of orthoclase shown in the norm being di- 
minished modally and replaced by leucite, while the amount of nor- 
mative albite is increased modally. Only the amounts of the more 
important constituents are given here. 
I II Til IV V VI Vil 
SLO Peer Bue oes U Fea sOe | SS O7 has Su | 54220 A qeoS8 al aosom laa oS 
INIA ONS as abe oe 23-74 20.85 19.07 19.38 109} 2 0X0) 14.51 TVG At 
e7 Oa eechs ney 0.63 2.34 OAL 3.83 2.88 2.151 4.09 
ie OF. 1.26 I.10 ere 2.14 aT Sake 4.24 
IY ie © hee cheater cae 0.81 0.48 1.98 I .35 9.19 Onn, 7 AO 
CA@mr: 0.67 3.07 3.15 2.15 9.65 9.04 One 
IN EVA Oe ca paee mice 5-29 4.81 FOF 8.01 222 B52 3 5 
KO: 10.05 10.49 4.84 5.28 4.96 5.60 5.00 
I. Grano-beemerose (nephelite-syenite). East Cape, Siberia. Washington, 
American Journal of Science, Vol. XI{I (1902), p. 176. 
II. Sabatinal beemerose (leucite-phonolite). Lake Bracciano, Italy. Wash- 
ington, Roman Comagmatic Region (1906), p. 47. 
III. Grano-laurdalose (laurdalite). Laugendal, Norway. Broégger, Erup- 
tivgesteine des Kristiantagebietes, Vol. III (1899), p. 19. 
IV. Phyro-laurdalose (leucite-rhombenporphyry). Kilimanjaro, East Africa, 
Finckh, Rosenbusch Festschrift (1906), p. 392. 
V. Grano-shonkinose (shonkinite). Yogo Peak, Little Belt Mountains, 
Montana. Weiedand Pirsson, American Journal of Science, Vol. L (1895), p. 474. 
VI. Leucite-shonkinose (leucite-shonkinite). East Peak, Highwood Moun- 
tains, Montana. Pirsson, Bulletin No. 237, U. S. Geological Survey (1905), 
p. 108. 
VII. Leucite-phyro-shonkinose (analcite-leucite-basalt). Highwood Peak. 
Highwood Mountains, Montana. Pirsson, op. ct. p. 168. 
It may be thought that the slight differences observable in some 
of the constituents, especially in silica and potash, may account for 
the differences in the modes, at least in part. But study of the norms 
and the modes, so far as these latter are exactly ascertainable from the 
descriptions, shows indubitably that these chemical differences are 
entirely too slight to bring about the very great divergencies between 
the modes of the several pairs of rocks. The amounts of orthoclase 
and nephelite in the one, and of leucite and albite in the other member, 
