174 ; WILLIAM J. MILLER 
The sulphur appears too low in the analysis as judged by the 
amount of pyrite visible even to the naked eye. 
The high TiO, shows either ilmenite or that the magnetite is 
decidedly titaniferous (most likely the former), though a little of 
the TiO, may be in the biotite. 
TABLE IV 
Chem. Comp. Norm Mode 
SIO irae 50.57 Ot eee eon Plagioclase..... 40.78 
ALON res lie 1133.5 Sie) Orth eee oe: Rit ,U2 NICS cho so oco Do 2S 
HeO Wee 3.26 Zatth otter cee te 0. Ske 24.10 Biotiteae eee sesO 
SLO) esis rsI4 18) 3a 10.09 ANIOIES Nonicrote oo 31 18.63 Jilmentitetan seem OnSG 
Mp Qire cisterna 4.98 NaCI ake ae 52 Pyrite n secs Tapia 
CaO ban hiaer Nae 7.07 Miao ices ie anu 4.64 Quartzeeeeaeeeer 52 
NaZOe nies 2.92 U baste sey eel Mera cack RO? ANOMBS Go cg5c05 oO 
IKE OA ON ye eeyat 1.89 JA pal ty: Piaatateabens .67 
Oe ee aa a4) PIMOT ee ce .16 
LBRO R tiaimaio aoe arcey Diop sk esis 14.44 
ABO Sls oe wicia eee 2.68 IEHY NER a Sono 00 08 17.41 
BO Se austere .28 ISLOR See bosueo  Ubiee 
(eat a MeAl area .09 
1 Ea Reade pee ae .09 
IM Gal O}abeoanti un AN 36 Class III Order 5 Rang 3 Subrang 
BaO eee FENN OO Salfemane Gallare Camptonase | Camptonose 
STO Ue heen .10 
Sota ner naetet ae .03 
Motal ee MOONS 
It is important to note that the typical gabbro and diabase 
are almost exactly the same in chemical composition (both being 
camptonose) except for somewhat higher silica and lower lime in 
the diabase, this difference probably being due to the slightly 
more acid character of the plagioclase in the diabase. Thus, 
these two rocks have quite certainly been derived from the same 
basic source of supply, though at different times. 
CAUSE OF THE PRIMARY VARIATIONS OF THE GABBRO 
APPLICATION OF DALY’S MAGMATIC STOPING HYPOTHESIS 
What has caused the remarkable primary variations of the 
gabbros? The writer believes there is strong evidence favoring 
the application, to a greater or lesser extent, of Daly’s magmatic 
stoping and assimilation hypothesis to the solution of this problem. 
