Logiealmond slate quarries, Highland Border slate belt, Scotland
|From: Richey, J.E. and Anderson, J.G.C. 1944. Scottish slates. Wartime pamphlet No. 40. London : Geological Survey of Great Britain.|
Logiealmond: Craiglea Quarry
Six inches to the mile: Perth, Sheet 84 N.W.
|Locality||Three quarters of a mile N.W. of Logiealmond Lodge, 9 ml. N.E. of Crieff.|
|Access||By road to Logiealmond Lodge, thence by service road.|
|Description of slate||Colour mainly bluish-grey, with some green bands: surface even, slightly rough; texture medium; striping due to bedding frequently present; pyrites practically absent. A few thin quartz veins in places.|
|Dips, with amounts||Cleavage-dip W. 35º N. at 60º. Bedding-dip: the main part of the quarry has been worked in a syncline of bedding with a steep, short limb to N.W. dipping S. 35º E. at 70º and a gently inclined longer limb to S.E. dipping W. 25º N. at 40º. A complementary anticline can also be distinguished on N.W. side of the quarry. The folds have a slight pitch to S.W.|
|Joints||A few, generally rather flat joints occur.|
Details of workings
The quarry lies about 1,500 ft. above sea-level and has been driven into the hillside from the S. and then expanded to the N.E. and S.W. It is now an excavation about 135 yds. in diameter at the top, tapering down to about 15 to 20 yds. in diameter at the bottom. Its mean depth is about 150 ft., and its maximum and minimum depths about 200 and 100 ft. respectively. There is a gallery about 60 ft. above the floor, which is not now continuous around the quarry.
On the N.W. face of the quarry, where there is a band of rusty-weathering fine to medium-grained grit, the slates are much obscured by debris and by the effects of surface creep. To S.E. the slates are interbedded with thin gritty bands and are probably of poor quality. Overburden in the form of drift deposits is absent, but the slates are weathered to a considerable depth.
Owing to the factors just mentioned, extension to N.W. or S.E. appears to be impracticable. On the N.E. side of the lower portion of the quarry the slate seems solid and of good quality and might be worked forward for a short distance, but the ground falls away in this direction. Moreover, as shown on (P519823) , a fault is believed to cut out the slate-rock a short way N.E. of the quarry, as grits are encountered in this direction in a nearby stream. At the S.W, end of the quarry, there is slate of apparently good quality on the N. but quality appears to be poorer on the S. side. There are therefore probably reserves to S.W. at the bottom level, although it should be noted that, owing to the pitch in this direction, the gritty band which occurs high up on this face might soon descent on top of the slates.