590 EDWARD SAMPSON 



the cherts be accumulations of radiolarian tests they can hardly 

 be considered as oozes. 



Vulcanism continued to a moderate degree into the Caradoc, 

 but, as in Notre Dame Bay, cherts are not found in the rocks of 

 this age. The geological history of the two regions is strikingly 

 similar. 



These examples, which might be multiplied, serve to show the 

 wide distribution of cherts associated with volcanic rocks, and it 

 is believed that in some instances, where volcanic rocks do not 

 form part of the chert-bearing sections, vulcanism may have been 

 nearly contemporaneous with the chert formation without its 

 products appearing with the cherts. An example of such conditions 

 is seen in the chert-bearing sections in Badger Bay of Notre Dame 



Bay. 



Are Cherts Radiolarian Oozes? 



G. J. Hinde, the foremost student of the radiolaria, regarded 

 radiolarian cherts as lithified oozes, and continually used the 

 presence of radiolaria as a criterion for determining the deep water 

 origin of the rocks containing them. That the cherts are deep 

 water deposits has often been questioned, due to the common 

 association with black graptolitic shale, and to the occasional 

 association with sandstones. 



That the radiolarian cherts of the Franciscan Group were not 

 deposited in extremely deep water has been shown by E. F. Davis. 

 He says: 



The Franciscan sandstone [the principal member of the Franciscan Group] 

 is a medium, coarse-grained sandstone which appears to be, in large part, of 

 continental origin. None of it was laid down far below sea level. In the 

 neighborhood of San Francisco, there are two formations of radiolarian chert 

 which divide the sandstone into three formations. If we regard the cherts as 

 abyssal radiolarian oozes, like those of the present day, we must believe that 

 the region sank from sea level to a depth of from 12,000 to 15,000 feet, and that 

 this tremendous displacement occurred twice within Franciscan time, with 

 two reversals of movement.^ 



The association of some of the radiolarian cherts of southern 

 Scotland with greywackes has already been noted (pp. 16-17). 



' Op. cil., p. 362. 



