424 The American Naturalist. . [May, 
This fact, together with the absence of phenocrysts near the peripheries 
of the dyke indicates to the author that the large feldspars are not of 
intratelluric origin, but that, on the contrary, they were formed in place. 
The paper closes}with descriptions of a quartz tinguaite-porphyry and 
_ several pseudoleucite-sodalite-tinguaites. 
Rocks of the Laurentian area north of Montreal.—Adams* 
has examined carefully the geology of the Southern portion of the 
Archean protaxis of North America that lies in the western portion 
of the Province of Quebee. The rocks occurring in the area studied 
belongjto the Grenville series and to the Fundamental gneiss. The 
former are present in a series of bands of alternating gneisses, quarzites, 
limestones and anorthosites, with occasional bands of pyroxene amphi- 
_bolites, pyroxene-gneisses, etc. All these rocks have been described? in 
other papers, but not as fully as they are described in this one. 
The Rocks of the Leucite Hills.—Kemp* describes the Leucite 
Hills in southwestern Wyoming as the remains of a volcanic crater 
formed in later Tertiary time. These hills and several of the buttes in 
their vicinity are composed of flows of what was once a very fluid lava 
followed by upwellings of a more viscous magma. The rocks of the 
different flows vary in character. Some are extremely rich in leucite. 
In others sanidine replaces this mineral, and in specimens obtained from 
Black Rock butte phenocrysts of augite and olivine are plentiful. The 
rocks in which leucite is most abundant consist almost exclusively of 
this mineral and biotite. In the feldspathic rocks the quantity of 
leucite decreases as the sanidine increases. Augite is also present in 
these varieties sometimes as inclusions in the sanidine and at other 
times as large colorless crystals surrounded by rims of biotite. The 
rock of Pilot Butte, about 22 miles southwestern of the Leucite Hills, 
consists of large colorless crystals of augite and plates of light brown 
mica in a groundmass composed of a felt of augite microlites and a few 
leucites in a glass matrix. It is evidently closely related to the leucite 
rocks (leucite-phonolites) though mineralogically an augitite. 
The Rocks of the Columbretes, Spain.—The rocks forming 
the little group of islands off the east coast of Spain, known as the Col- 
umbretes, are trachytes, trachytic-phonolites, tephritic trachytes, bas- 
alts and palagonite tuffs according to Becke.” The feldspar of the tra- 
* Geological Survey of Canada. Ann. Rep., Vol. VIII. Pt. J. 
5 AMERICAN NATURALIST. 1897, p. 564, 1896, p. 300 and 579. 
Bull. Geol. Soc. Amer., Vol. 8, 1897, p. 169. 
7 Min u. Petrog. Mitth., XVI, p. 157 and 808. 
