312 The American Geologist. 
November, 1905 
REVIEW OF RECENT GEOLOGICAL 
LITERATURE. 
The secondary origin of certain granites, R A. Daly. (Am. Jour. 
Sci., vol. 20, Sept. 1905.) 
This paper throws much light on the manner of origin of cer- 
tain acid igneous rocks. In the prosecution of the survey of the 
international boundary between Canada and the United States, in 
the region between Port Hill, Idaho and Gateway, Montana, are 
found enormous thicknesses of quartzytes associated with argillytes. 
Dr. Daly here found numerous sills of gabbro lying parallel in the 
stiata, some of the sills having a thickness of 2,500 feet, while the 
sedimentary rocks afford a total of about 20,000 feet of bedding 
exposed to geological study. The sedimentary rocks are divided 
into Creston quartzyte (at the bottom), the Kitchener quartzyte 
and the Moyie argillyte. 
The sills, where in their present normal condition, were found 
to consist of hornblende gabbro, with some accessory quartz, titanite, 
biotite, and a little orthoclase. While this is not a gabbro it is 
assumed by the author to be the primary intrusive magma that 
entered the sedimentaries. These accessories increase as the rock 
varies from its original composition in the vicinity of the planes of 
contact with the sedimentary rocks, especially the orthoclase, 
quartz and biotite, accompanied, also, by microperthite. There is, 
further, a variation in the structural relations. The quartz becomes 
poikilitic to all the other constituents except the orthoclase and 
the microperthite, and with these it forms a micrographic inter- 
growth. 
These phenomena are most marked in the greatest sills, the 
largest being denominated the Moyie sill, rather more than 2500 
feet in thickness. While the quartzytes have been thoroughly 
metamorphosed, and especially feldspathized, near the sill, the 
gabbroid rock has been more profoundly altered. This alteration 
is most extensive along the upper contact of the sill, where the 
hornblendes are obliterated and in the place of labradorite is the 
feldspar andesine. Biotite is much increased in amount and soda- 
orthoclase also occurs, along with much quartz; microperthite, 
micropegmatyte, calcite, muscovite and epidote are also found along 
the contact. At fifteen feet from the upper contact hornblende is 
still wanting. The same is true of labradorite; oligoclase is 1.0 per 
cent, soda-bearing orthoclase is 32.5 per cent and quartz 41 per 
cent. There is also muscovite and titaniferous magnetite. At 50 
feet from the upper contact, while hornblende and labradorite are 
still wanting, oligoclase constitutes 1.5 per cent and orthoclase 24.9 
per cent. Quartz is here 57. per cent, and calcite 2.5 per cent. At 
.'200 feet from the same contact hornblende is 49.4 per cent, biotite is 
