Description of Plate VI. 



Plate VI. shows three microphotographs of the Montville rhyolite 

 in ordinary light. 



Fig. 1. — Rhyolite in microslide 261a, from Bon Accord Falls. It shows 

 the spherulitic structure very well, also the very fine 

 cryptocrystalline groundmass. The spherulites have a 

 radial structure, and are composed of kaolin much stained 

 with limonite. Ordinary light. Magnified X 50. 



Fig. 2. — Rhyolite in microslide 264, from Skene's Creek, ^-mile below the 

 Bon Accord Falls. This shows the small rods and granules 

 of haematite which occiir so abundantly throughout the 

 hypohyaline groundmass. The white patches represent 

 felspar fragments and holes. Ordinary light. Magnified 

 X 35. 



Fig. 3. — Rhyolite in microslide 473 from Bon Accord Falls. It shows the 

 oval to rounded character of the hoUow spherulites, the thin 

 walls of which show a radial arrangement of rod-like forms 

 and the interior a nucleus of " secondary" quartz. Ordinary 

 light. Magnified X 50. 



