Abstract
Locality. These specimens were obtained from the Porphyrite formation, which for the most part divides the Lower Old Red Sandstone of the great centre valley of Scotland from the Clay Slate and Greywacké of the southern highlands. The exact locality of these agates is a small tributary of the Shaggie, on the left bank, and about three hundred yards north of the schoolhouse at Monzie. (See sketch map adjoining.) Proceeding up this stream from A towards B, as marked on the sketch, we find some interesting variations in the contents of the rock. Association. 1. At A a reef of Carytes runs for some yards on the left bank of the stream. I am inclined to think this reef persists probably as far as B, as I find there in the bed of the stream fragments of the mineral. 2. Further on just above the point where an old road (now disused) crosses the stream, we find amygdaloidal porphyrite. The rounded enclosures of this are mostly calcite, but here and there they are composed of red or blue chalcedony, and some of them are true agates. 3. Still further up the burn we reach the place where the specimens about to be described are found. 4. Then again, about the old road to Sma’ Glen, the rock is intersected by jasper veins. Common Characteristics. 1. Irregularity of shape—so markedly different from the rounded, oval, or flattened form of the common
Published Version
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