CHERT FORMATIONS OF NOTRE DAME BAY 



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ner. This structure is most readily explained as caused by precip- 

 itation by diffusion. The whole sectem is now composed of crystal- 

 line quartz, the boundaries of the grains showing no relation to the 

 structure described. Another part of the same section is illustrated 

 by Figure 4. The clear central areas contain minute cherry red 

 plates presumably of hematite. The boundaries of these crystals 



Fig. 2. — Thin section (No. 211) of jasper from Sweeny manganese prospect, For- 

 tune Harbor. Shows banding in what is thought to have been colloidal silica. Section 

 now composed of quartz whose crystalline structure is entirely independent of the 

 original structure of the rock. Magnified 100 diameters. 



as seen with the microscope are very sharp. It is only possible to 

 get a few in focus at one time to photograph. Outward from these 

 crystals is a clear ring bordered by a transitional cloudy zone grading 

 into the opaque ring. This ring is in turn surrounded by a clear 

 ring and the whole inclosed in opaque jasper. The crystals are 

 interpreted as having been formed by a segregation of iron oxide 

 from the now clear nucleus while the whole was in a gelatinous 

 state. 



