TERTIARY FORMATION. 651 
has a light grayish feldspathic base, and is thickly spotted with trans- 
lucent crystals of feldspar one to two thirds of an inch long, besides 
mica, and hornblende in small black crystals; this is the syenitic 
oneiss just alluded to. ‘The same rock occurs of reddish and purplish 
shades. Another form of the porphyry is laminated, the laminz being 
very thin and easily separable: it contains mica, arranged parallel 
with the plains of lamination. 
This laminated porphyry has, at times, a porcelain aspect ; and some 
specimens consist of an alternation of chalky and compact layers. In 
other parts the fine lamination is rendered distinct by a difference 
in shade of colour. One block was broken which consisted of deli- 
cate stripes of white, light sepia brown, and bright purple colours. 
Glassy feldspar and hornblende are frequently disseminated with the 
mica through this laminated rock, though less abundantly than in the 
compact trachytic porphyry. 
The outer slopes of the belt were covered with loose masses of the 
compact rock, and layers of the same constituted the belt ridge. 
These slopes are intersected by ravines made by water, as well as by 
the passages described. 
In the annular valley, near the passage that opens through the belt 
eastward, there is an isolated hill, about one hundred and twenty feet 
high, and four hundred and fifty in diameter, the surface of which 
consists of large blocks of grayish and reddish trachytic porphyry 
lying loose, some of them eight cubic feet in size. 
The Bute was evidently a volcanic cone. It is probable that the 
centre, at some period in its history, fell in, leaving only the lower 
part of the slopes entire. As rocks and fragments from ejections are 
not found over the prairie around, it was extinct before the river flats 
were formed; and the overflow of the river has since filled up and 
levelled off the surrounding country, as well as a large part of the 
annular plain. ‘The bill of trachytic blocks near the eastern entrance 
may have been one of the later points of eruption. As the cone is 
partly buried in the river detritus, we evidently see only a portion of 
its original elevation, and it may be but a very small portion. 
Tertiary Formation. 
We have already stated that the tertiary formation of Oregon occurs 
in various places from Puget’s Sound to San Francisco, along the 
