58o EDWARD SAMPSON 



stone and then moistened. This test was found useful in the field. 

 In one bed near the westernmost point of Gull Island, the radiolaria 

 appear like abundant white sand grains in the red matrix of the 

 rock. 



The cherts of this locaHty show almost no radiolaria. It is 

 believed that these chert beds were formed much more rapidly 

 than the enclosing shales, and that they are free from radiolaria 

 and impurities because of this rapidity of deposition. 



COMPOSITION AND STRUCTURE 



To avoid repetition, the green varieties of chert will be described 

 together followed by a description of the red varieties. There is a 

 fundamental relation between the present color of the chert and the 

 manner in which it has been formed. 



Green Chert 



Green chert is found in the first and third types — ^interstitial 



and thin-bedded. In both types it appears to be of much the same 



nature. Most thin sections show an extremely fine aggregate of 



interlocking grains of quartz, the largest grains in different thin 



Analysis of 2-inch Bed of Green Chert 

 (260 Y 16 a) FROM West Side of Law- 

 rence Harbor, Ship Run, Bay of 

 Exploits, Notre Dame Bay, 

 Newfoundland 



SiO^ 85.78 



AlA 5-68 



Fe^Oj 2 . 92 



FeO 2 . 09 



MgO .25 



CaO 48 



Na.O 68 



K.0 .36 



H,0± 1.88 



100 13 



sections varying from about 0.05 mm. to as little as 0.02 mm. In 

 every case most grains are considerably smaller than the largest, 

 generally about 0.005 i^^^- Some sections contain isotropic silica 

 and in these there is a gradation from the isotropic area into the 

 crystalline area, crystallization starting at scattered nuclei. 



