Notes 071 Monhegan Island. — Lord. 
343 
II 
74.21 
■ 30 
14 
(soda-ganulyte) from near Mariposa, California,* is reproduced 
for comparison. 
I 
Si02 74.78 
TiO. 
AI2O3 14.56 
Fe203 3.04 
FeO , 
CaO 69 
MgO trace 
Na^O 6.02 
K.O 59 
Ign 42 
P2O. 
47 
35 
50 
71 
28 
62 
10 
38 
07 
Total 100.10 99-99 
Spec, gr 2.64 
The rather large amount of iron in I may be attributed to 
the presence of garnet and cordierite; the latter mineral being 
frequently altered to a fibrous mass (pinite?) strongly impreg- 
nated with limonite. 
In other respects both analyses are essentially identical. 
The abnormally high percentage of soda and silica com- 
bined with but .69% CaO clearly indicates an acid member 
of the albite group (Abi2:Ani) as the principal constituent of 
the rock. 
The basic dikes of the area are of special interest as they 
may be taken to represent products of deep seated differentia- 
tion peculiar to the noryte magma. Dikes of quite similar 
character are by no means rare and have received careful treat- 
ment by various authors- + 
*See H. W. Turner: 17th Ann. Rept., U. S. G. S., Part I, p. 721. 
tSee F. D. Adams: op. cit., p. 434, Rept. on the Geology of the 
Laurentian Area of Montreal. Ann. Rept.. Geol. Soc. Canada, Vol. 
VIII, 1895, pp- 134-139- 
G. H. Williams: The Gabbros and Dioritcs of the "Cortlandt 
Series." op. cit., p. 442. 
J. F. Kemp: Gabbros on the Western Shore of Lake Champlain 
(jp. cit., p. 223. and A Diorite Dike at Forest of Dean, Orange Co., N. 
Y.. Amer. Jour. Sci., XXXV, 1888, p. 331. 
W. D. Matthews: op. cit., p. 197. 
W. S. Bayley: The Eruptive and Sedimentary Rocks of Pigeon 
Pt., Minn., U. S. G. S., Bull., 109, 1893, p. 44. 
