256 The American Geologist. ^p^'"- ^^^^ 
d. Effusive rocks, consisting of two flows of basalt. 
The average composition of all the rocks described is calculated 
to be that of an acid syenite approaching a monzonite in character. The 
rocks of the laccoliths here, as nearly everywhere in the Rocky moun- 
tain region, are usually porphyritic and acid. They are typical exam- 
ples of Rosenbusch's granitic porphyritic dike rocks, which are here 
typically laccolithic. The phenocysts appear to have been formed 
where they now are, and in no case to have been brought up from 
greater depths. No differentiation has been noted in the laccoliths. 
Yogo peak and the porphyries east of it are examples of differentiation 
in place, the centre of the mass being acid and the periphery basic. The 
tendency is here shown for acid rocks to be porphyritic, and basic rocks 
imder the same conditions, granular. Chemical composition, not depth 
of intrusion, is seen to be the determining factor of granularity. 
Numerous small syenite-aplite dikes cut the Yogo mass. They rep- 
resent the acid residuum forced up into the fracture planes of the upper 
and previously solidified rock. 
The report closes with a discussion of magmas by graphic methods, 
and of absorption of sediments by magmas. The chemical composi- 
tions of the Yogo peak rocks are shown to bear a mathematical relation 
to one another, which points to a common origin. 
This area presents no facts in favor of the view that large amounts 
of sediments ma}' be absorbed by magmas and produce alterations in 
composition of igneous rocks. i. H. 0. 
Notes on the Limestones and General Geology of the Fiji Islands, witli 
special reference to the Tazu Group. Based upon surveys made for 
Alexander Agassiz. By E. C. Andrews. {Bull. Mus. Comp. Zool. 
of Harvard College. Geol. Surzry, vol. v, No. i. Pp. 1-46; with 
40 plates.) 
This paper represents a more careful examination of some of the 
problems suggested to Mr. Agassiz in his exploration of Fiji in the 
winter of 1897-8. Further results brought in by the W. S. F. C. S. 
"Albatros," yet remain to be worked up. Mr. Agassiz expects shortly 
to publish a final report upon the islands. 
The present paper consists of careful descriptions of the different 
beds accompanied by excellent illustrations and maps. The islands are 
a group of atolls which in Tertiary, and again in recent time, were 
subject to volcanic activity. The limestones are indurated in some lo- 
calities and soapstone is found. There is a decided excess of igneous 
over calcareous rock. i. h. o. 
Contributions to the Geology of Maine. By H. S. Willi.\ms and H. E. 
Gregory. (Bui. U. S. G. S. No. 165.) 
A report upon the fauna of Maine was greatly to be desired for pur- 
poses of comparison between the typical forms of New York and of 
Canada, and also as a basis of correlation between American and Eu- 
ropean Paleozoic phases. This paper deals with sedimentarj' areas in 
Somerset and Aroostook counties, and with the Aroostook volcanic 
area. 
