THE STEUCTUEE OF EOCK MASSES. 
235 
dislocated, whilst immense fragments of them are detached and 
enclosed in the mass of light-coloured granitic gneiss ; and, as 
further evidence of its eruptive nature, fig. 6 shows how, at 
Haukeraadalen, this granitic gneiss throws out a small vein 
breaking through the adjacent hornblende schist and possessing 
all the structural characters of true granite, and entirely wanting 
the parallel lines of foliation seen dipping invariably at a high 
angle to the east in the main mass of granite gneiss. Similar 
cases have been described by Keilhau in other parts of Norway, 
and by Scott and Haughton in Donegal. 
Even in the most characteristic eruptive granites, it is not at 
all uncommon to find portions of the rock possessing a more or 
less defined parallel structure, due to the position of the plates 
of mica in them, in consequence of which the rock, to use the 
workmen’s language, 66 has a grain,” and splits more easily in 
this direction — a feature which — as, for example, in some parts of 
the Aberdeen white granite quarries — is made use of for the 
purpose of making curbstones, &c. The lithologist, on seeing 
such stones, would describe them, and correctly so, as granitic 
gneiss, although petrologically — that is, studied en masse in the 
field — they are true granite. In Germany the distinction gneiss 
granite has been employed for such undoubted granites as 
possess a foliated structure. 
The direction of the lines of foliation was for a long time 
regarded as that of the original stratification, and in many in- 
stances, no doubt, this is the case ; for example, in the section 
Tig. 3. 
a, a. Ordinary gneiss. b, b. Toliated pink crystalline limestone. 
c, c. Bands of augitic gneiss in the limestone. 
a, a. G-ranite veins, each ten feet thick. 
shown in the annexed woodcut, which is taken near Christian- 
sand, and which shows alternating beds of ordinary and augitic 
gneiss with foliated crystalline limestone, which are without 
doubt the representatives of sedimentary beds of silicious and 
calcareous nature, originally deposited by water, and broken 
