CHERT FORMATIONS OF NOTRE DAME BAY 579 



age, but they are in marked contrast with those of the Franciscan 

 Series of California. This type of chert in Notre Dame Bay 

 commonly contains radiolaria. 



The tuffs associated with the chert are composed largely of 

 crystal fragments among which quartz usually predominates. 

 Both potash feldspar and soda-rich plagioclase are present together 

 with a considerable amount of fine-grained devitrified glass. All 

 the fragments are angular and are contained in a very fine-grained 

 ground-mass. Delicate structures such as shards of glass seem to 

 be entirely lacking, the material probably having been sufiiciently 

 waterworn to have destroyed them. Beds of shale are common, 

 but many of them are of a peculiar nature, perhaps originally 

 containing some gelatinous silica. The whole chert, shale, and 

 tuff series is frequently associated with pillow lavas. 



In one place chert of the thin-bedded type is found where there 

 are no volcanic rocks in the section, but there is reason to believe 

 that these chert beds were formed contemporaneously with volcan- 

 ism elsewhere in the district. In Badger Bay, on the small islands 

 south of Gull Island, a section is found which resembles those of 

 Leading Tickle and Lawrence Harbor and like them is in close 

 proximity to beds of black graptolitic shale. On these islands 

 thin beds of chert are well exposed, but the tuffs which form parts 

 of the other sections are absent. However, the black graptolitic 

 shale fixes the age as contemporaneous with the volcanic rocks of 

 the other sections. 



This section, which probably represents about 2,000 feet of 

 sediments, is composed largely of varieties of a peculiar shale. 

 In the hand specimen it is a hard dense rock, where cleavage is not 

 highly developed. The commonest colors are green and gray. 

 It is rather thin-bedded and free from carbonate. In parts of the 

 section, portions from 50 to 100 feet thick are predominantly red 

 and in or near these red portions thin-bedded chert is found. There 

 is probably a considerable admixture of cherty silica in these shales. 



The most interesting feature of these red shales is the great 

 profusion of radiolaria at some horizons. The shale rich in radio- 

 laria usually shows them in the hand specimen as light specks. 

 These can readily be seen if the rock be smoothed off with a whet- 



