1922] Whitman: Genesis of the Ores of the Cobalt District 303 



are found crusts, often beautifully crystallized, consisting of proustite 

 or argentite, or dyscrasite, or perhaps native bismuth, these crystalline 

 masses coalescing with and blending imperceptibly into typical ore 

 in the adjacent veins. 



CONCLUSION 



In this account and discussion of the geology at Cobalt the two 

 principal points which I have intended to make are that the fissures 

 in which the ores were deposited were not cooling cracks in the strict 

 sense, but were joints developed as a result of folding subsequent to 

 the solidification of the diabase, and that the ores were derived from 

 the diabase sheet itself, transported, and deposited chiefly through 

 the agency of diffusion through relatively stagnant water in the pore 

 spaces of the rocks. 



The folds, which affect diabase and sediments alike, are parallel 

 with the major structural axes of the region and also with the original 

 undulations of the diabase sheet which transgress the sedimentary 

 beds, these folds being indicated in the diabase by innumerable large 

 and small surfaces of shearing parallel with the surface of folding. 

 The vein joints are spatially related to the folds and to the faults 

 which originated during the folding. From these relationships it is 

 inferred that such joints are genetically related to the other deforma- 

 tions and to external compressive stresses rather than to direct cooling 

 shrinkage. It is immaterial, and impossible to conjecture, whether 

 this compressive stress arose chiefly from the lateral expansive force 

 due to the heating of the locality of the sheet, or whether it arose 

 chiefly from the general contraction due to the cooling of the locality 

 of the sheet, the latter having an undulating configuration, and the 

 undulations being weak to lateral compression resulting from the con- 

 traction of their general environment. Since all the deformations, 

 however, are clearly of the same immediate period as those in the 

 diabase, the conclusion seems inevitable that the diastrophic activity 

 followed the solidification of the igneous mass, and was of a compres- 

 sive character. 



In connection with the genesis of the ores it was pointed out that 

 the commercial veins of the whole region as well as those in other 

 parts of northern Ontario lie exclusively within marginal zones of 

 the Nipissing diabase extending not more than 350 feet inward and 

 outward in the diabase and Keewatin formations, nor more than 550 



