p 
TRANSACTION S 
OF THE 
PERTHSHIRE SOCIETY OF 
NATURAL SCIENCE. 
I .—Outcrop of Diabase at Rossie Priory. By R. Dow. 
(Read 14th December, 1893.) 
The Sidlaw Hills throw a flood of light upon the forces of nature 
at work during the Old Red Sandstone period. Whilst on the one 
hand that system was being slowly deposited by the action of water, 
another force came into play to give variety to the monotonous 
process. Volcanoes seem to have broken out through the sandstone, 
and to have spread their ejected molten material on the bed of what 
must have been an inland sea. In the intervals of quiescence be¬ 
tween these outbursts the sandstones, grits, and conglomerates were 
deposited over the volcanic layer, hence that alternation of sandstone 
and igneous rock so characteristic of the Sidlaw range generally. 
Out of this mass of volcanic and sedimentary deposits the familiar 
features of the Sidlaws have been channelled and chiselled by the 
ordinary forces of nature. These have cut up and carved the range 
into peak and crag, ravine and den. 
This well-known range extends in a north-easterly direction from 
Kinnoull Hill into Forfarshire, keeping parallel with the strike of 
the sedimentary deposits of the Old Red Sandstone. From Kinnoull 
Hill (729 ft.) to the King’s Seat (1235 ft.), the highest peak of the 
range, the distance is nine miles. The range maintains a fairly 
uniform breadth of three to four miles, but in the vicinity of the 
border line between the counties of Perthshire and Forfarshire it 
sudden*^ contracts in breadth to half these dimensions. The range 
continues still eastwards, and thins out to its termination towards the 
centre of Forfarshire. In the great natural recess formed by the 
thinning down of the range is to be found that small corner of our 
county which forms the subject of this short paper. 
A 
