10 FRANK D, ADAMS 
No. 7. Diorite—Big Timber Creek, Crazy Mountain, Montana 
(Wolf Bull USGS, 148, ps TAA TSo7): 
No. 8. Normal Essexite—Mount Johnson, Quebec (Adams, 
Jour. of Geol., April-May, 1903). 
The silicated portion of the half-altered limestone (Analysis 
t 6), which in the quantitative classification would fall under Auver- 
genase, has certain igneous rocks which approach it rather closely 
in composition, although it is higher in lime than any igneous rock 
whose analysis has been hitherto recorded, as emphasized by the fact 
that akermanite appears as a standard mineral in its norm. ‘The 
following igneous rocks resemble it most closely: 
I II Il 
SIO eee 48.11 40.15 40.16 
A OF aes 16.98 Ba ks7/ 13.86 
He @ yer c/linde | eackecs 3.61 5.26 
WOE 5. Oe 8.15 TAL 
MnoO.. TOO™ 4 vil, + te chemepleor alll pee mccstearas 
MgoO.. 5.67 12.63 11.60 
CaO 7) als TE IES 15-74 
Nit @ etic 1.82 1.29 I.05 
DES ©) ear ra ence a age ase nee OEMESEeee ©. 30 
FETE Qe ee er Le ey se Oa LN pe EAT 3.40 
100.03 100.55 99.18 
I. Saussurite gabbro, Yttero, Norway. 
Il. Hypersthene gabbro, Urals, Russia (Loewinson-Lessing, G. 
Sh. Jushno Saos, Dorpat, 1900, p. 166). 
_ III. Gabbro (not fresh), Laurion, Greece (R. Lepsius, Geol. 
v. Atttka, Berlin, 1893, p. 98). 
In connection with this alteration of limestone to amphibolite 
it is to be noted that the change is not one of solution or digestion 
of the limestone by the granite, for the fragments preserve their sharp 
and well-defined forms even when the alteration is complete. 
The limestone, at a distance from the granite, is a white crystalline 
marble, containing scarcely any impurities and effervescing freely in 
fragments with cold dilute hydrochloric acid, showing that it is an 
essentially pure carbonate of lime. 
The granite which brings about this alteration has not been 
analyzed but is in all probability of essentially the same composition 
