If such surfaces are thus produced, undoubtedly the 

 faces of pebbles and boulders in moving masses of rock are 

 also grooved and striated in such a way as to be undis- 

 tinaruishable from those of arlacial origin. 



Lorrain Arkose; and Quartzite:. 



As explained on a preceding page the arkose and quartz- 

 ite, to which the name Lorrain has been applied, are here 

 grouped with the Cobalt series, and are considered to 

 represent the upper members of the series. In two or three 

 localities, the arkose and quartzite have been found to be un- 

 conformable to the slate-like greywacke or other lower 

 members of the series, but in other places there is no evi- 

 dence of an erosion interval. Since, however, the arkose 

 and quartzite in most of the areas that have been mapped 

 tend to occur distinct from the lower members of the series 

 they are distinguished on the maps, by a different color, ; 

 from the latter. 



Frequently the arkose is found on the surface of granite, 

 e.g., in the township of Lorrain, and is the decomposition 

 product of the latter rock, there being a gradual passage 

 from the undecomposed rock into the arkose. There is, 

 moreover, a gradual passage upward from the arkose, first 

 into impure quartzite, then into a purer quartzite and con- 

 glomerate, composed chiefly of quartz pebbles. 



THE NIPISSING DIABASE 



The diabase, to which the name Nipissing has been 

 given, occurs characteristically as a sill. At Cobalt much 

 of the hanging wall of the sill has been removed by erosion, 

 and the diabase occupies about one-half of the surface of 

 the productive area, the sill dipping on the whole at a low 

 angle to the southeast. From following descriptions, how- 

 ever, it will be seen that the din of the sill is much steeper 

 at certain points. 



In the region 5,000 square miles or more in extent, that 

 surrounds Cobalt, the diabase occupies a considerable 

 percentage of the area, and is seen in many cases to be in 

 sill-like form. Owing to the association of cobalt ores with 



