84 The American Geologist. Febraarj, ifoo 
Granite-porphyry . — Somewhat similar in compostion but 
yet quite distinct from the granites, are certain dikes of a 
feldspar porphyry, locally known as "birdseye" porphyry- 
They are characterized by large distinct crystals of white felds- 
par embedded in a fine-grained mixture of quartz, orthoclase 
and plagioclase feldspar, and sometimes a little mica. Al- 
though the presence of the latter mineral is not often readily 
apparent to the unaided eye, it is generally represented in 
widely scattered and very small foils, connecting the "birds- 
eye" porphyry with the granitic series. 
This is one of, if not the oldest of the porph}ries. In the 
Upper Cofifee creek district, a great dike of it, often out-crop- 
ping to a width of several hundred feet, persistently follows the 
Lawrence fault, w'hile other dikes occur at a short distance on 
either side. I am strongly inclined to consider the granite- 
porphyry of this area as of the same age as the folding and 
faulting of the stratigraphic series and possibl}- slightly older 
than the grano-dioryte and Courtney granite. Its dikes can be 
traced close up to the latter, but never into it. 
The "birdseye" porphyry varies much in texture and even 
in composition. One variety of it contains, in addition to the 
large white feldspar cr\-stals, distinct, needle-shaped crystals of 
black hornblende which often cross each other near one end at 
an acute angle, giving rise to the miners' names of "bird's-foot" 
porphyry, "crow's-foot" porphyry, or even "turkey-foot" por- 
phyry. Dikes of this variety generally occur to one side of the 
main granite-porphyry dikes, and may be the result of a dififer- 
entiation of the same magma, although of slightly dififerent 
age. 
Pegmatyte. — Dikes of a white, muscovite granite occur in 
the Courtney granite and the adjoining hornblende schists at 
the head of the south fork of Salmon river. They are cut by 
diroyte-prophyryte and diabase dikes, but are distinctly young- 
er than the true granite and grano-dioryte of the same region. 
Quaiiz-porphyrytc. — In the Upper Coffee creek district 
there are narrow dikes of a rock of white color, fine grain and 
a general appearance like ciuartzyte. That the\- are not a meta- 
morphosed sedimentary is proved by their occurrence in dike- 
hke masses of irregular width, distinctly cutting the lines of 
original stratification in the schists. I'urthermore, they are 
