Cherts and Dolomites. Bill 
per cent. of metallic iron, titanium being absent.’ The 
specimens were found to exhibit magnetic polarity in 
different degrees, this characteristic being also brought to 
light du1ing the field surveys by the great local derange- 
ments of the magnetic needle. Small particles of pyrite 
are also frequently disseminated throughout these rocks. 
An interesting variety is the “ pitted chert.” A consider- 
able exposure will often be found pitted all over with little 
rounded cavities about the size of a pea. These present a 
rough and hackly inner surface, and are frequently par- 
tially filled withiron-rust. A variation of the phenomenon is 
presented in the occasional presence in the thin cherty lay- 
ers, sometimes found interbedded in the argillites, of tubules 
at right angles to the surfave of the layer, which, apart 
from the difference in shape, present much the same details 
of appearance as the cavities of the pitted cherts. Dr. Bell, 
in his report on this district, notices a very similar pheno- 
menon. He says: “ Nearly horizontal calcareous beds 
occur containing small coral-like siliceous concretions and 
vertical cylinders of chalcedony, transverse sections of which 
shew fine concentric rings resembling agate.” ” 
Whilst calcareous matter is specially the characteristic 
of the upper argillites and shales, it is not entirely absent 
from the rocks under consideration, being present as a 
mineral resembling anthracite often found in the centre of 
vuggy cavities in the rocks. 
In both upper and lower divisions calcarecus and dolo- 
mitic areas are frequent, although not constituting a pre- 
ponderating feature of the formation. In the argillaceous 
division the earthy carbonates are frequently present to 
such an extent as to give free effervescence with acid. In 
the lower siliceous division areas are frequent, made up of 
this calcareous and dolomitic material, which is often fer- 
ruginous, as shewn by the rusty appearances of weathered 
surfaces. At one place a fine-grained, grey dolomite was 
found to contain what appeared to be rounded pebbles of a 
1 Annual Rept. Geol. Surv. of Canada, Vol. IIL, p. 25 T. 
? Report of Progress, Geological Survey of Canada, 1866-69, p. 324. 
