THE COBALT SERIES; ITS CHARACTER AND ORIGIN 123 
Along with the older complex the Cobalt series is intruded by the 
Nipissing (Keweenawan ?) diabase which took the form of dikes 
in the older basement but spread out as sills in the flat-lying 
Huronian sediments. 
The third structural subdivision, the Pleistocene and Recent 
deposits consist of gravel, sand, and bowlders, in the various forms 
assumed by glacial and fluvioglacial materials, and stratified clay 
and sand of postglacial lacustrine origin. These rest on the 
beveled surface of the Cobalt series or on the truncated surface 
of the older complex from which the Cobalt series has been stripped 
away. 
THE COBALT SERIES 
GENERAL CHARACTER AND SUBDIVISIONS 
The Cobalt series consist of an assemblage of clastic sediments, 
conglomerate, greywacke, argillite,’ arkose, and quartzite. These 
rocks are not sharply defined members, for they not only pass 
gradationally into one another, both horizontally and vertically, 
but conglomerate commonly occurs in the midst of greywacke or 
greywacke in the midst of conglomerate, and a similar relationship 
may exist between all the members of the series. Nevertheless, 
in a general way, there is a succession in most localities, from a 
basal conglomerate through greywacke and argillite to arkose, 
which in turn is overlain by an upper conglomerate. 
A compilation of all the published observations of the suc- 
cession and thickness of the various rocks comprising the series 
throughout the Timiskaming region is given in the accompanying 
table. Many of these sections are evidently only partial, including 
in some cases the upper members and in others the middle or 
lower. It can be seen, however, that there is generally an upper 
and lower conglomerate with greywacke and argillite, quartzite, 
and arkose as intermediate members. 
«At the suggestion of Dr. L. V. Pirsson, the term argillite is here redefined to 
designate a fine grained slate-like rock which has been very firmly cemented but has 
no slaty cleavage. Its position in the mud-slate series corresponds very closely to 
that of quartzite in the sand-sandstone group. 
