REPORT OF TEE CHIEF ASTRONOMER 

 SESSIONAL PAPER No. 25a 



151 



.-slate. They may be as much as four or five centimetres in diameter but the 

 average diameter is under one centimetre. Many are well-rounded but most 

 •were subangular at the time of deposition. Occasional phases show some flat- 

 tening of the pebbles by orogenic pressure, though the degree of shearing and 



Figure 11. — Drawing from thin section of metamorphosed argillaceous 

 sand-stone, Wolf formation. Large grains are quartz except the 

 partly shaded one in southwest quadrant (microperthite). Quartz 

 shows cataclastic structure and some secondary enlargement. 

 Ground-mass of quartz and sericitic mica. See text. Diameter of 

 circle, 5 mm 



mashing never, even distantly, approaches that represented in the Irene con- 

 glomerate or in the lower zones of the Monk formation. Here, again, many 

 of the pebbles (some as large as 5 mm. or more in diameter) are made up of 

 fragments of single quartz crystals, apparently indicating the great coarseness 

 of the granitic rock which furnished this immense body of silicious detritus. 

 The single-crystal pebbles, as well as others of compound and granular texture, 

 are greatly strained, with the result that they are often of the peculiarly rich 

 -blue or gray-blue opalescent colour noted in the Monk conglomerates. 



