LIMITATIONS OF PRE-CAMBRIAN NOMENCLATURE 327 
Cambrian province and at points hundreds of miles from those in 
which these names were originally defined, would seem to imply 
that our knowledge of the succession of formations within this vast 
territory was much more complete than is actually the case. Only a 
very small part of the territory in the St. Lawrence basin in which 
pre-Cambrian rocks occur has been actually mapped in detail, and 
even in those localities which have been mapped in considerable 
detail and have been regarded in the past as type areas the suc- 
cession of formations formerly supposed to be present has in many 
cases been considerably modified by more recent investigation. 
THE PRINCIPLES OF, PRE-CAMBRIAN CORRELATION INAPPLICABLE 
OR INADEQUATE 
Continuity or approximate continuity of outcrop.—The principle 
of continuity, or approximate continuity, of outcrop is the most 
conclusive of all the means by which the relationship of rocks can 
be determined. But it is inapplicable to the correlation of the 
various rock series occurring in the different pre-Cambrian sub- 
provinces for the reason that these are geographically and in part 
geologically separate from one another. Between the Timiskaming 
and the Grenville subprovinces there intervenes an extended belt 
of banded gneisses; between the Timiskaming and the western 
subprovinces there are the little-known wooded pre-Cambrian 
highlands on the north and overlapping Paleozoic sediments on the 
south; and between the northwestern and the southwestern sub- 
provinces lie the waters of Lake Superior. If, therefore, a common 
nomenclature be employed for all the pre-Cambrian subprovinces 
of the St. Lawrence basin, this nomenclature must be based on other 
less conclusive principles of correlation. 
Lithological similarity —This criterion has been widely applied 
in the correlation of pre-Cambrian formations, although it is in 
reality of very limited application; for the pre-Cambrian rocks of 
1 A. C. Lawson, Geol. Surv. Can., Mem. 28, 1912, and Mem. 40, 1913, p. 4. 
W. G. Miller and C. W. Knight, Aun. Rep. Ont. Bureau of Mines, XXII, Part 2, 
1914. 
R. C. Allen and L. P. Barrett, Jour. Geol., XXIII (1915), 680. 
W. H. Collins, Geol. Surv. Can., Sum. Rept., 1916, p. 183. 
C. R. Leith and R. C. Allen, Jour. Geol., XXIII, 703. 
