IP UW BLECA LIONS. 
Notes on some Eruptive Rocks from Gallatin, Jefferson and Madison 
Counties, Montana. By GrorGE P. MERRILL, Proc. U. S. 
National Museum, Vol. XVII., pp. 637-673, Washington, 
1895. 
In these notes Professor Merrill has described some of the more 
interesting rocks of those collected by Dr. A. C. Peale and himself in 
the parts of Montana named in the title. The notes are arranged 
according to the geographical occurrence of the rocks rather than 
upon a petrographical basis, which latter would have been more con- 
venient for reference. The rocks are in part extrusive, including 
basalt, several kinds of andesite and rhyolite; and in part intrusive, 
embracing a wide range, from syenite and diorite to peridotite and 
pyroxenite, and including a number of porphyritic rocks some of 
which are lamprophyres. 
The andesites are normal for this region and are only briefly 
described. In the case of a hypersthene-andesite a complete chemical 
analysis is published. The rhyolites and basalts are normal, except for 
a quartz-bearing basalt like those found in other parts of western 
America. Diabase and diorite of various kinds are briefly mentioned. 
Several peridotites are described in considerable detail. They occur 
in areas of crystalline schists but appear to be of eruptive origin. The 
rocks are classed as wehrlite, hornblende-picrite, saxonite (harzburgite). 
Closely related to them in composition and mode of occurrence are 
certain pyroxenites, one of which is hornblende-hypersthenite, while 
another is websterite. The value of these descriptions is enhanced by 
complete chemical analyses, which fortunately have been made from 
very fresh material. 
The special interest of the paper lies in the description of a 
number of lamprophyric rocks and of closely associated syenitic 
porphyries; besides several porphyritic rocks described as porphyrite 
(2), augite-porphyrite, and in one case as basalt (?) These descrip- 
tions are full and embrace the chemical composition of the rocks and 
also of some of the more prominent constituent minerals. One class 
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