Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/458



PLATE 17.

Represents a more perfect example of the red lines which are found in the limestone, and these serve at the same time as indications of the bending which the limestone has undergone. Minute granite veins resembling in their composition these red parallel lines are found traversing the fragment of schist, which has lost its usual conformable parallelism to the calcareous bed.

PLATE 18.

Is selected as a representation of that utter confusion among the substances contained at the junction which almost eludes the powers of the pencil. It contains examples of all the variations which in the former drawings have been separated from each other, and in addition to those is shown an instance of the compression of the limestone bed.

PLATE 19.

To preserve uniformity in the colours which represent the different rocks I have here also tinged the limestone blue. It is white in nature. It serves to show the entire loss of the stratified character which the limestone so often undergoes in the vicinity of the granite. Specimens from this junction are also in the Society's collection.

PLATE 20.

The sections in this and the next plate are intended to represent the relative positions of the rocks, and they are founded on numerous observations throughout the Glen. The alternations are not laid down as real, nor is there any pretence to conjecture dimensions which could not be measured.

Fig. 1. Represents the case occurring at Gow's bridge where the limestone and schist are found on each side of the river. It may be said that the water has not yet wrought its way to the junction.

Fig. 2. Represents the case which predominates throughout Glen Tilt. The river here divides the stratified rocks from the granite, and has exposed the various junctions which are laid down in the map and described in the paper. It is easy to see how these will sometimes consist of limestone, sometimes of schist or of quartz rock, and sometimes of all the three substances, with the granite.

Fig. 3. Represents the case which occurs at Cairn a'chlachan, as well as in numerous other situations, and it explains the otherwise puzzling phenomenon of the apparent alterations between the quartz rock and the granite. It is easy to see that the schistose strata, once possibly lying much higher on the granite, have remained in some places while they have disappeared in others.