HURONIAN FORMATIONS, TIMISKAMING REGION. 
21 
Some idea of the length of time represented by this break 
may also be gained by comparing the unconformity referred to 
in this quotation with that in, say, Whiskey Lake area. The 
structural relations of the over- and underlying formations are 
the same — gently folded Huronian sediments resting upon 
maturely eroded surfaces of closely folded sediments and schists, 
and invasive granite-gneiss — ^but in the case quoted the over- 
lying sediments are the upper of the two Huronian series, while 
at Whiskey Lake they belong to the lower series. From a con- 
sideration of the structural features of the unconformity alone 
the time intervals represented in the two areas might be the 
same, yet the interval at Whiskey lake is actually less than that 
near Sudbury by the time required to lay down sedimentary 
materials 2,740 feet thick, In other words the whole time inter- 
val is so great that a portion of it requisite for the deposition of 
2,740 feet of conglomerate, quartzite, greywacke, and limestone 
is too insignificant to find perceptible expression in the character 
of the unconformity. 
The Upper Huronian Series. 
The slate conglomerate group in Bruce area is composed 
largely of formations of peculiar appearance. It includes a 
boulder conglomerate which bears a distinct resemblance to a 
consolidated boulder clay and contains^ occasional striated 
boulders (Plate I). It includes also a laminated greywacke, or 
finely stratified argillitic formation consisting of layers of fine- 
grained, slate-grey greywacke one-fortieth to one-quarter inch 
thick that vary slightly in shade and give the rock a characteristic 
delicately laminated appearance. A conglomeratic phase of this 
laminated greywacke which carries occasional pebbles of granite, 
etc. , up to 8 inches in diameter, is even more distinctive of the group. 
The only deposits of recent times comparable to the laminated 
gre3rwacke and laminated greywacke conglomerate are the strati- 
fied boulder-containing clays laid down in post-Glacial lakes. 
The whole group is 2,600-3,000 feet thick and the individual 
formations in it vary notably in thickness and in order of suc- 
cession in different parts of the area. 
