I9I4.] CONCEPTION AND TRINITY BAYS, NEWFOUNDLAND. 393 



the centers of the nodules or occurring as intercalated lenses or 

 nodules in the nodular bed is found to be essentially a maganiferous 

 calcite (see Analysis C, page 395). 



Fig. 17. Microphotograph of coalescing nodules from 219 A6c; slide 

 243 ; enlarged 4 diam. a, carbonate of manganese, etc. ; b, oolitic shale. 



Further macroscopical examination of the nodules shows the 

 presence of barite blades within the central portions of the nodules or 

 disseminated throughout the nodule or its shaly matrix. The char- 

 acteristics which determined the barite arc its c and m cleavage, its 

 hardness of 2 and its diaphaneity. Its optical properties confirm it 

 microscopically. Pyrite is found sometimes completely surrounding 

 central cores as irregular and continuous grains. The surfaces of 

 the nodules usually are covered with minute pink or reddish dis- 

 seminated grains which upon microscopic examination are found to 

 be hematitic spherules. 



Thin sections of these nodules, on the whole, are not satisfactory 

 for microscopical work because of the almost impalpable fineness of 

 the grain. However some of the larger features may be of interest 

 and importance. The structure is nodular and concentric and some 

 of the concentric shells are oolitic. In all the thin sections of 

 nodules the most conspicuous feature is the zonal arrangement of 

 crystalline and indeterminable portions. The crystalline parts 

 usually occupy the centers of the nodules while the impalpable or 

 indeterminable areas are arranged around the centers (see Fig. 16, 

 Slide 288). However some of the cores consist of indeterminable 

 material. The zones are sometimes marked ofif from each other by 

 more or less sharp contracts as brought out by a difference in shade 

 of color or by an apparent difference in grain (Figs. 17, and 18). 



