EXPLANATION OF THE PLATES. 



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 junc- 

 tion are also in the Society's collection. 



P L A T E 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. Repi'esents 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 througliout 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 pheno- 

 menon of the apparent alternations 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. 



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