328 M. E. WILSON 
the Canadian shield, both sedimentary and igneous, are for the 
most part common types which might be deposited or intruded or 
extruded in any epoch of earth history. It has been largely on the © 
basis of this principle that the name Keewatin, first applied by 
Lawson to the metamorphosed basal volcanic complex occurring 
in the region northwest of Lake Superior, was extended, first to 
the Timiskaming region and later to eastern Ontario, a district 
nearly 1,000 miles distant from the locality in which the term was 
originally defined; yet volcanic rocks of this character are among 
the most common in the earth’s crust. They are represented at 
some point in nearly all the pre-Cambrian series of the St. Lawrence 
basin; are likewise abundant in later formations throughout the 
world, as in Great Britain, where they occur at numerous horizons 
ranging in age from the early Palaeozoic to the Tertiary; and are 
in process of formation at one or more points on the earth’s surface 
today. Asa consequence of this unscientific method of correlation 
the name Keewatin, although presumed to represent a definite 
formation, in reality is now applied in the Canadian pre-Cambrian 
subprovinces to any highly metamorphosed volcanic rock without 
regard to age. 
Similar stratigraphical succession of beds.—The larger part of 
the pre-Cambrian surface rocks of the region under consideration 
are volcanic flows or clastic sediments, in which a regular sequence 
of strata is uncommon, and this criterion is therefore inapplicable 
except to the late pre-Cambrian rocks. It has been especially 
useful in the mapping of the Huronian series in the Timiskaming 
subprovince, the Lower Marquette in the region south of Lake 
Superior, and the Animikie sediments in the region northwest of 
Lake Superior. 
Similar serial succession.—The widespread correlation implied 
in the nomenclature applied to the pre-Cambrian rocks of the 
St. Lawrence basin has been based to a considerable extent on this 
principle, although the apparent similarity in the serial succession 
may very frequently be explained in other ways. The principal 
objection to the use of this criterion is that it neglects to consider 
the possibility of overlap. Sedimentary rock series are not gener- 
ally deposited continuously or uniformly over immense areas, and 
