1922] Whitman: Genesis of the Ores of the Cobalt District 257 



Proustite, breithauptite, dyscrasite ; a long- list of unimportant silver 

 and arsenic and other minerals is also recognized. The areal geology 

 of the district has been mapped by Miller and Knight 2 and the reader 

 is referred to their map. 



DESCRIPTIVE GEOLOGY 

 The Pre-Cobalt Surface 



The basement complex upon which the Cobalt Series was deposited 

 is here referred to as the Keewatin, since that is the local usage. Its 

 eroded surface has been found in the Cobalt area to be remarkably 

 smooth and flat, such irregularities as may exist being much smaller 

 than any of the hills of the present surface. One of the original 

 irregularities is a low knob on the north end of Cobalt Hill about 2000 

 feet northeast of the low-grade mill of the Nipissing Mining Company, 

 where the conglomerate of the Cobalt Series may be seen lapping 

 unconformably against the lower slopes. Another irregularity occurs 

 as a depression exposed by the workings of the Seneca Superior Mine. 

 Other minor ones have been found here and there in the mines of the 

 district, but they are never comparable in size with the major undula- 

 tions caused by folding. Probably the Cobalt, Prospect, McKinley- 

 Darragh, Lawson, and other hills of the district are not original 

 irregularities on the Keewatin surface, but are anticlinal folds. 



In the course of my studies I constructed a contour map of the 

 contact between the Keewatin and the Cobalt Series (see fig. 1). 

 When the dips of the overlying sediments were superposed, they were 

 found to conform to the slopes of this surface. Although the slopes 

 lie between 10 and 30 degrees, the deptli of the sediments and the 

 exactness of their parallelism with the lowest layers would seem, to 

 exclude the possibility of sedimentation on slopes, since this condition 

 persists for several hundred feet above the contact. 



Further evidence that the major undulations of this contact are 

 due to folding lies in the fact that when the dips of a certain set of 

 flatly inclined joints were plotted upon the formational contour map, 

 they coincided with the contoured slopes, and with the dips of the 

 beds overlying them. These flatly inclined joints are of a type pro- 

 duced by shearing stresses during the folding of rock masses, and are 

 parallel to the warped or folded surface. 



2 Ontario Bureau of Mines, Report, (XVI), 1907. 



