CHERT FORMATIONS OF NOTRE DAME BAY 



585 



ORIGIN 

 COMPARISON WITH OTHER REGIONS 



Before taking up the origin of the cherts, it will be well to 

 compare them to similar formations elsewhere. . In reading the 

 literature of this subject, one cannot but be greatly impressed by 

 the abundance of chert formations which are similar in many 

 respects to those of Notre Dame Bay. Such formations have a 



Fig. 4. — From same thin section as Figures 2 and 3. Show segregation of iron 

 oxide into hematite plates and also original banding outside the area of segregation. 

 Magnified 430 diameters. 



very wide distribution both in area and in geologic time. E. F. 

 Davis^ has recently given a thorough review of the literature 

 describing the types of chert here under discussion so that any 

 extended review here is unnecessary. A most strikingly uniform 

 feature of the descriptions is the intimate association with volcanic 

 rocks. Pillow lavas usually form a part of the section, although, as 

 in Notre Dame Bay, the chert itself is usually interbedded with shale 

 or tuff. The following will serve as examples. 



' E. F. Davis, "The Radiolarian Cherts of the Franciscan Group," 5w//. Univ. 

 Calif., Vol. XI (1918), No. 3, pp. 235-432. 



