PETROGEAPHICAL CHARACTER OF THE WEWE SLATE. 267 



The uovaculites are similar to tlie slates and graywacikes, except that 

 they are largely composed of very small, rounded grains of quartz and 

 fewer of feldspar, of a somewhat uniform size, with a very sparse matrix 

 of sericite, kaolin, and ferrite. In the field these uniformly granular 

 fine-o-rained rocks were not discriminated from the secondary chert veins 

 and layers, but in thin section they are wholly different, having the grains 

 distinctly rounded and not closely fitting, and having the sparse matrix 

 above described. The cherty material, upon the other hand, consists of 

 finely granular, perfectly fitting quartz, free from the clayey constituents, 

 and where iron oxide is present, it is usually concentrated to a greater or less 

 deo-ree in bunches or layers, rather than uniformly disseminated between 

 the ])articles, as in the novacidites. 



The quartzites, iuterstratified with the higher members of the formation, 

 are in all respects like the Ajibik quartzites hereafter described. 



The graywackes, slates, and uovaculites, as has been indicated (pp. 

 260-2G3), have frequently had developed 'in them a slaty cleavage or schis- 

 tose structure, and have been broken tln-ough and through 1)y dynamic 

 action. As a result of this, crevices and cracks have formed parallel to the 

 bedding, parallel to the secondaiy structures which intersect the bedding, 

 in directions independent of either of these, and between the individual 

 particles of the rocks themselves. These cracks and crevices have been 

 largely cemented by finely crystalline, perfectly fitting grains of quartz, 

 which in hand specimen has a cherty appearance. In other places coarsely 

 crystalline vein cjuartz has entered. During the readjustments cracks have 

 laro-ely formed parallel to the bedding, and secondary cherty layers ha\-e 

 formed in this direction. In hand specimen, in some cases, they might be 

 regarded as truly interbedded layers, but when examined in thin section 

 the secondary character of this vein chert is undoubted. This is shown 

 l)y the fact that within it are fragments of the onginal slate, and also from 

 these apparent quartz bands smaller veins of cherty quartz ramify, cutting 

 the slate in all directions. Moreover, as examined in hand specimen, these 

 chert-y-looking layers often have a lenticular character, the oval layers lying 

 end to end or overlapping. In one case, where the secondary coarsely 



