278 



ME. J. S. GAEDKEE OX THE LEAF-BEES 



and a few small flakes of biotite. Its specific gravity is 2'50. The 

 felspar gives, by Szabo's method, the reactions of a soda-orthoclase, 

 and the rock may be classed as fairly with the sanidophyres (or 

 sanidine-felsites) as the preceding specimen with the trachytes. 

 The occurrence of a lava of this composition makes one hopeful 

 as to the future discovery of nepheline-bearing rocks in Mull. 



"We may conclude, then, that during the deposition of the Ardtun 

 gravels, when only the first of the basaltic outpourings had taken 

 place, a number of earlier flows must have been still available as 

 sources of material. The chalk-downs which probably then existed, 

 as evidenced by the flints that form so large a portion of certain 

 beds, were themselves overlain by the products of the central cones, 

 the fragments worn from both the aqueous and the igneous series 

 becoming intermingled in the hill-side streams. 



Gr. C. 



Externally in the ravine this gravel weathers to almost the colour 

 of the Trap, and the bedding of the shingle is not apparent ; but the 

 clean freshly blasted surfaces showed the flints altered to a pure 

 white against the steely grey colour of the matrix, which is here so 

 hardened that even the very small pebbles break across when it is 

 fractured. 



These gravels are easily traceable for the next 120 or 130 yards 

 across the bluff to the west of the ravine, and the leaf-bed can be 

 followed for about half the distance, though greatly concealed by 

 grass. Here there is another ravine (fig. 4), where the entire 

 thickness was reduced to 14 feet, the sands being distinctly bedded 

 and laminated, and none of the pebbles in the gravel much larger 

 than a filbert. Another good exposure occurs a little further west, 



Pig. 4. — Exposure in Second Ravine, Ardtun Head. 



where the thickness appears to be reduced to 12 feet, and then the 

 sedimentary rocks are almost wholly concealed by talus and grass, 



