THE PRECAMBRIAN ROCKS OF THE CANTON QUADRANGLE 23 



to be merely transitional to the thin-bedded quartzites. The quartz- 

 mesh limestone is a rock made up, in its typical development, of 

 quartz and calcite in nearly equal proportions. The two minerals 

 are distributed in such manner that the quartz forms a complex 

 system of irregularly forking and anastomosing lines, and the calcite 

 occupies the intervening detached areas. Plate 3, upper figure, 

 shows the characteristic texture and structure of this remarkable 

 rock. 



The quartzite streaks, often preserving glacial pohsh and striae, 

 have here weathered in relief, and on first glance present the appear- 

 ance of a compound quartz vein, or a group of interlocking quartz 

 veinlets cutting the limestone. The mesh of this structure, however, 

 is rather more uniform than would be expected if the quartz were 

 of hydatogenic origin, for the spacing of the meshes remains un- 

 changed throughout a considerable thickness of strata, and in the 

 direction of the strike is even more uniform. The variations which 

 throw most light on the origin of the quartz-mesh rock are those 

 which take place stratigraphically, that is, in the different horizons 

 of the formation. The quartz becomes increasingly abundant, the 

 meshes flatter and more elongated, while at the same time the lime- 

 stone filling gradually disappears, till a thin-bedded, often highly 

 crumpled, quartz-schist is developed (see plate 3, lower figure). 



The transition between the two is complete, and the quartz-mesh 

 rock is most reasonably viewed in the light of an unusual sedimen- 

 tary type rather than as a system of unusually regular quartz vein- 

 lets. On the other hand, the method by which the quartz became 

 segregated in the limestone to form such a uniform and unique 

 structure is difficult to conceive ; but the probability of its being re- 

 crystalHzed clastic material originally present in the limestone seems 

 quite certain. 



Another locality where this mesh structure is well developed is on 

 the right side of Harrison creek, about four-tenths of a mile north- 

 east of the road. The quartz schist transition phase is absent, and 

 the nature of the formation at this point would be indeed difficult 

 to account for, were the occurrence above described not available 

 for comparison. 



