257 
intrusive sheets in the sandstone, whilst another part has come 
into existence from subordinate beds of impure sandstone or 
argillaceous material. It is not impossible that in some cases 
a transference of matter from the magma to the sediments may 
have taken place. A circumstance pointing in this direction is 
the not unusual occurrence of fluorite and crystallized hematite 
in fissures in the sandstone, even far away from the line of 
contact. Some of the hornfels sheets may perhaps have been 
enriched with iron in this manner, and the graphite may per- 
haps be of pneumatolytic origin. 
Under the microscope the hornfels beds appear to be of an 
extremely varying composition, and not two specimens have been 
found alike. The number of minerals to be seen in thin sec- 
tions is very large, but on account of their small size of grain 
their identification is often difficult or impossible. We will only 
refer to a few instances here. 
A specimen which seems to represent an entirely re-cry- 
stallized igneous sheet shows large scales (about 1 millimeter) 
of chocalate-brown biotite irregularly distributed over a very 
fine-grained mass. This consists of a micro-crystalline aggre- 
gate of twinned felspar grains mixed with a number of other 
minerals, among which a fibrous greenish hornblende and a 
colourless mineral having the qualities of the clinozoisite are 
most conspicuous. Apatite needles are tolerably abundant, iron 
ore only occurs in relatively large irregular grains surrounded 
by biotite. Small cracks in the rock are filled by analcime and 
a little fluorite. 
In another specimen which is probably of similar origin, the 
biotite is of a brownish-green colour mixed with brown garnet, 
granules of iron ore, titanite, and a large quantity of pale green 
augite. The latter is partly in relatively large anhedra which seem 
to be remnants of the original augite of the rock, and partly in 
small rounded grains. Among these minerals lies a colourless 
aggregate of felspar and alteration products of same. 
XXXVIII. 17 
