354 
Mr. Playfair’s Account of a 
one of the former kind, of great breadth, cuts it right across 
from NE. to SW. not far from the point of its greatest eleva- 
tion. There is no where any appearance of metallic veins. 
The quartzy rock of Schehallien is extremely hard and ho- 
mogeneous, and by its slow and uniform decay, has no doubt 
given rise to that massive shape, and comparatively unbroken 
surface, which have been already remarked. Yet even here 
the work of time is abundantly evident ; for the rock being 
much cut by fissures transverse to its stratification, it separates 
and falls down in large prismatic fragments. Some of these 
are of a vast size, and being extremely durable, the accumu- 
lation of them where the ground is not too steep to permit 
them to lie, is very great, so that large tracts of the sides of 
the mountain are covered with cubical blocks of granular 
quartz, resting on one another, and steadied only by their 
own weight. 
It is remarkable of this quartzy stone, that when exposed for 
some time to the weather, it acquires the lustre and appearance 
of white enamel, so that the old weather beaten surface is more 
clear and shining than that which is immediately produced 
from a fresh fracture. The reason seems to be, that the stone 
does not consist of pure quartz, but along with the grains of 
quartz has a great number of grains of felspar interspersed, 
which when it is first broken give it an opaque and earthy 
appearance. These are soon dissolved by the action of the 
weather ; and there is then left over the surface a coat of pure 
quartz, which has the semi-transparency and vitreous gloss 
belonging to enamel. 
The felspar which enters into the composition of the rock 
here described, is not always in grains, but in some specimens, 
