Synchroiiisia of the Lnke Superior llegion. — Winchell. 211 
M((p of the Lake Superior Region. 
The accompanying map of the Lake Superior region (plate 
XI) is designed to show the approximate areas of land and 
water at three different times in the progress of events as 
above projected, throughout the Lake Superior basin. 
The areas designated by A represent the land at the close 
of Archean time, or just prior to the opening of Taconic time. 
As the Taconic seems to have been inaugurated by a wide- 
spread submergence, as indicated by the extensive conglom- 
erate which forms its base, even at points somewhat remote 
from its present surface boundaries (which themselves may be 
supposed, however, to have been driven back by degradation 
some distance from their original positions) it is probable that 
the land areas at the close of the Archean were considerably 
larger than here shown. It is, however, obviously impossible 
to even approximate a correct representation of the actual 
Archean land in those tracts which are still buried beneath 
sediments of Cambrian and later date. This map therefore 
shows simply a representation of Archean areas that are now 
known to be exposed at the surface. The term Archean here 
covers all the basal crystalline complex which is found in a 
crumpled condition unconformable below the Taconic and 
which has been divided by Lawson into Laurentian, Couchi- 
ching and Keewatin. It iru'ludes the lower iron-bearing rocks 
of the Lake Superior region, but not the upper. 
Areas designated by T show the land increments due to 
rocks of Taconic age, including in this the areal extent of the 
eruptives of the Norian and of the Keweenawan, the latter of 
which brought Taconic time to a close. The ditliculty of map- 
ping the later eruptives as an integral i)art of post-Taconic 
time is the principal reason for putting them with the Taconic. 
Again they are so intimately associated with the earlier erup- 
tives and with the nu'tamorphic c(»nditions of the clastic 
strata of the Taconic of which they embrace large masses, 
and between the planes of which they have penetrated as con- 
formable layers, that to separate them in sucli a inaj) would lie 
impossible. (Chronologically they are i)()st-Taconic,antl on their 
upper surface lies tlie l)ase of the rocks of the I)icell(»ce]thalus 
zone. They simply form a punctuation (latum in geological 
history, belonging as much to what prccinles as to that which 
