124 The Sedimentary, Metamorphic, 



were invaded from below by molten masses, which acted 

 especially upon such areas as those referred to in conclusion 

 3, and also generally upon the argillites, producing the con- 

 tact schists. 



(5.) The period when the Ensay schists were formed may 

 be placed at the close of the Silurian age, and in any case 

 cannot be later than the close of the Middle Devonian 

 period. 



EXPLANATION OF PLATES III. AND IV. 



Fig. 1. Horizontal section of schists at Ensay, about eight 

 feet in width, (a) Schist, (b) quartz vein, (c) crystal- 

 line-granular intrusive rock. 



Fig. 2. Horizontal section showing relation of schist and 

 pegmatite vein, (a) Schist, (b) pegmatite, (c) aplite.- ... 



Fig. 3. Horizontal section of schist and crystalline-granular 

 rock at Ensay. (a) Schist, (b) crystalline-granular 

 rock. 



Fig. 4. Microscopical section of microcline-perthite prepared 

 from principal cleavage, (a) Microcline, (6) albite, * X 55. 



Fig. 5. Microscopical section of microcline-perthite prepared 

 from second cleavage, (a) Microcline, (6) albite, x 55. 

 The engraving gives the impression of striation in this 

 albite, which is incorrect. 



Figs. 4 and 5 drawn by polarised light. 



