198 REVIEWS 
may be judged from the report, the classification of the pre-Silurian 
rocks adopted by the survey is as follows: 
Cambrian (St. Croix, ‘“‘ Potsdam”’) 
(Upper Cambrian) 
Rees (clastic) 
and 
Taconic 
(Lower Cambrian) 4 
{ Keweenawan Manitou (igneous) 
oe (igneous) 
Animikie 
( eee ewan 
Archean 5 
Lower Kewatin 
I. ARCHEAN 
. Lower Kewatin.—The rock of the Lower Kewatin is in general 
ae by the survey as greenstone, and is composed of two 
divisions: (1) A lower massive igneous greenstone, assumed to repre- 
sent the original crust of the seth, and (2) an upper series, partly 
fragmental and partly chemical, including beds of basic tuff, of agglom- 
erate, and of conglomerate, the jaspilytes and iron ores of the Ver- 
million range, and vast masses of quartz-porphyry. Both the jaspilytes 
and the porphyry are tentatively held to be the result of chemical pre- 
cipitation in the Archean ocean, the apparent dikes of the porphyry 
in the Upper Kewatin being considered as infolded masses, or as intru- 
sions brought about by plasticity due to the subsequent application 
of heat and pressure. 
2. Upper Kewatin—The Upper Kewatin consists of a_ basal 
(Ogishke) conglomerate, overlaid by a series of graywackes, argillytes, 
and a single jaspilyte. The fragmental members are characterized by 
the presence in greater or less amounts of greenish material supposed 
to have been largely derived from the waste of the lower Kewatin, 
and from the Archean volcanoes. ‘The whole series is involved with 
the Lower Kewatin in vertical isoclinal folds. 
All the members of the Kewatin, both Lower and Upper, have 
been locally strongly metamorphosed, giving rise to clastic gneisses, 
schists, etc., where the action was simply one of recrystallization, and 
