ON THE CONSTITUTION OF THE GRANITES OF DONEGAL. 49 
We shall commence the description of the county with an account of the 
rocks observed in Innishowen, and proceed in a 8.W. direction from that 
barony. In the north of Innishowen the rocks consist of grits, crystalline 
limestones, mica-slate, and a variety of igneous rocks (greenstones and 
syenites). The whole of these rocks are contorted considerably about Culdaff, 
and from that to Malin Head they exhibit a consecutive section, of which the 
dips increase as you go westward, the beds being nearly horizontal at Culdaff 
and along the shore towards Glengad Head. 
The grits of this part of the county are true grits, not having been suffi- 
ciently metamorphosed to form quartzites until we reach a more westerly 
point. There are a few beds of potstone and soapstone scattered through 
the argillite beds, but they are not of so much importance as those found at 
Convoy, Crohy Head, and in other parts of the county. 
There is also found in the mica-slate a series of beds of chalcedonic 
conglomerate, which is very characteristic of this district. Of this conglo- 
merate the cement is micaceous, and the pebbles are mainly siliceous (of the 
chalcedonic variety), but consist also of feldspar and of portions of the mica- 
slate itself. Similar conglomerates to these are described by Mr. MacFarlane* 
as a characteristic feature of the Huronian Series of Canada, and of their 
Norwegian equivalents, called by Naumann the Tellemarken Quartz-formation, 
from the district of that name in the south of Norway. Keilhauf says of 
them, that they occur in repeated alternations with hornblende rock; the 
cement is micaceous, and the pebbles sometimes feldspathic, sometimes 
quartzose, and sometimes of still more varied natures. In some places, he 
says, the concretions are apparently imbedded fragments of the rock itself, 
as if it had been broken up and the pieces had been irregularly joined 
together. 
A description of conglomerates similar to these is to be found in the Reports 
of the Geological Survey of Canada; and we are of opinion that similar conglo- 
merates have been discovered by two of our number in Scotland, viz. by Sir R. 
Griffith at Anie, not far from Callander, and by Professor Haughton at the 
summit-level of the Crinan Canal. 
It is very remarkable that the igneous rocks, which, as has been said before, 
are very abundant in the county, are undoubtedly cotemporaneous with the 
sedimentary rocks of Innishowen. This fact is observable along the coast, 
but it is noticeable in the most striking manner between Buncrana and Carn- 
donagh, about five miles from the former place, the whole of the hills lying 
between Slieve Snaght and the Raghtin Mountains being composed of 
alternating beds of quartz-rock and syenite, dipping at a low angle to the 
eastward. This is beautifully exhibited in the mountain of Binmore, lying 
in the district of the Barr of Inch, close to the Mintiagh Lakes. This hill 
with the mountain Bulbin are terraced like the trap hills of Antrim; but on 
a close examination it is found that, although the whole face of the rock 
appears to be columnar, it consists of alternate beds of quartz-rock and 
syenite, as before described. The columnar structure of the former is due to 
the simultaneous development in it of three series of joints inclined to each 
other at angles approaching those of a regular hexagon. These joints are all 
* We should here express our acknowledgments for the assistance we have derived 
from Sir W. Logan’s and Dr. T. Sterry Hunt’s “ Report on the Rocks of Canada,” now 
in process of publication by the Geological Survey of that country; and from Mr. Mac- 
Farlane’s two papers “On the Primitive Formations in Norway and Canada,” ‘ Canadian 
Naturalist and Geologist’ for 1862. 
+ Grea Norvegica, pp. 430, 432. 
1863, E 
