250 The American Geologist. April, 1892: 
very striking to one only acquainted with granite in its usual 
form—a finely granular mass. The quartz is as usual, dissemi- 
nated, but the albite, the chief ingredient, is found in very large 
erystals. and the mica in sheets sometimes a foot or more in diam- 
eter. With these occur crystals of black tourmaline occasionally 
weighing several pounds, and magnificent spodumenes, ten, twenty 
and thirty feet long in the rock. Here too, are found bery], 
cassiterite (tin-ore), columbite, and other minerals often associ- 
ated with these. 
These intercalated veins of coarse granite weather less rapidly 
than the schists and consequently stand out in bold relief on the 
hillsides, their wreckage strewing the ground so as to convey the 
impression that the granite area is much larger than is really the 
ease. No massive granite exists in the Hills, even the central 
Harney peak being composed chiefly of schists. The veins run 
in some instances for long distances—many hundred feet or yards 
—but eventually disappear to be succeeded by others in parallel 
lines. ; 
The presence of the cassiterite in them has drawn attention to 
these schists almost to the exclusion of the other strata of the 
Hills. We will return later to this topic when treating of the tin. * 
ry. 
The eastern slates overlying and conformable with the schists 
compose the younger part of the axis already alluded to. They 
occupy the whole eastern side of the mass of the Hills, and like 
the older schists dip steeply to the east. They are hard and blue 
or dark grey, have no true cleavage, and weather into ragged 
peaks or edges. So far as it is known they contain no useful 
minerals. Vast beds of quartzite are found in them so massive 
as to justify calling them at times sandstone deposits. 
V3 
Both the formations above mentioned belong to those early 
ages of geologic history or rather legend, which are at present 
comprehended in the term ‘‘Pre-Cambrian.”” It would be more 
*It is worthy of remark in this connection that the stanniferous veins 
of Dakota are immensely older than those of Cornwall. The latter are 
all of post-Devonian age, and probably in some cases very much later 
than the Carboniferous. Indeed it would seem as if the process of the 
deposition of cassiterite were continuous, as it is not uncommon to find 
in Cornwall recent deer-horns so impregna ed with the mineral, that 
they are as rich as the average ore of the county. 
