140 
SCIENTIFIC NEWS. 
The first article in this paper treats of the granular quartz 
rock of the island of Jura. This, by some denominated 
granite, and by others, granular quartz, but by all who have 
hitherto described it, considered as a primitive rock, constitutes 
the principal and fundamental rock of the island ; in parti- 
cular, the three well known conical paps of Jura , of the height 
of 2500, or 2600 feet, are entirely composed of this mineral. 
Jt is disposed in regular uninterrupted strata, six or eight 
feet in thickness, and rising, for the most part, at a considera- 
ble angle towards the west. These strata do not appear to be 
traversed by veins, except of quartz, nor do they alternate with 
any other rock. On the shore, however, the dip and direction 
of the beds are observed to vary considerably. The minera- 
logical composition of this rock, presents several varieties. 
Sometimes it is extremely compact, being made up of grains 
of quartz, of various degrees of magnitude, united without 
cement. Sometimes, besides the quartz, it contains felspar, 
seemingly in rounded fragments, and often decomposed into 
clay. In one specimen, a manifestly water worn pebble of 
quartz is enclosed ; and, upon the whole, the rock may be 
considered as a kind of sand-stone, consisting of quartz and 
felspar, the former in the larger proportion. In some of the 
beds, the sand-stone passes into granwacke-slate, by mixture 
with pieces of mica-slate. From these circumstances, D. M. 
considers the quartz rock of Jura as a mechanical deposit 
formed from the fragments of older ones, and not as belonging 
to the Wernerian primitive class. According to Professor 
Jameson, however, this very rock rises from below the mica- 
ceous schistus ; we must therefore admit either that the mica- \ 
ceous schistus described by Professor J., is not primitive, or ; 
that the circumstances under which the primitive rocks were 
formed, were such as to exclude, at the same time, the pro- 
duction of a mixed mechanical deposit. 
The next article in this paper, contains some miscellaneous 1 
remarks on the geology of the island of Rona. The principal 
rocks that here make their appearance, are gneiss and hornblende 
rock(including, under the latter denomination, both hornblende- 
slate and greenstone-slate). Where these two rocks come in 
contact, the gneiss is irregulariy curved and contorted $ the 
gneiss 
