SCIENTIFIC NEWS. 
141 
gneiss is traversed by numerous ;*nd thick veins of graphic gra- 
nite, in which wolfram occurs. 
The district of Assynt, forming the western part of Sutber- 
landshire, is the subject of the next article. The mountains 
and higher ground of this district, consists of the same rock 
as the so called granular quartz of Jura, forming here, as in 
the last mentioned island, smooth conical hills of considerable 
elevation, snow white at their summits, and singularly sterile 
and arid. The white colour of the rock, is, however, only 
superficial, the recent fracture exhibiting grey, yellow, and 
brown tints. It is distinctly stratified, and rises at a high 
angle. The texture of this rock is various, from imperfectly 
conchoidal, to loosely granular, composed of rounded grains, 
and in some beds of angular fragments. It divides naturally 
into rectangular blocks, on the surface of which, is the appear- 
ance, as if of cylindrical bodies imbedded in the moss, forming 
a number of circular protuberant spots, of a whiter colour, 
and more compact texture, than the rest of the rock. A sec- 
tion at right angles, to the natural surface of these blocks, 
shews that the above-mentioned circular spots are occasioned 
by the cross fracture of strait cylindrical bodies, which are, 
perhaps, the remains of some species of sabella. Associated 
with this grit, are compact gneiss, hornblende-slate, and syenitic 
granite, but their relative positions, D. M. was unable to ascer- 
tain. Subordinate to, and apparently alternating with this grit, 
is a great deposit of limestone, in two very thick stratified beds, 
with a thick bed of grit interposed. In some parts, the section 
of these beds forms a continuous and even line ; but in other 
parts, is so curved and broken, that the stratification can 
scarcely be perceived. 
The limestone is dark, grey, or nearly black, of an earthy 
aspect, and minute granular fracture, and smelling offensively 
when rubbed. It does not appear to contain organic remains, 
but is traversed by veins of red or white calcareous spar; it 
contains grains of sand, and, therefore, gives fire with steel. Its 
surface is covered, for the most part, with a loose calcareous 
tufa, which, in some places, being rendered solid by an infiltra- 
tion of calcareous matter, constitutes a hard breccia. 
In the same valley of the Tain, of which the above rock 
forms the precipitous side, occur insulated masses, rising through 
the 
