F. B. Bradley— Geological Map of the United States. 287 
of representing with more uniform accuracy areas which have 
been surveyed with more and with less minuteness. 
Considerable portions of the metamorphic areas heretofore 
mapped as Archean have recently been proved to be Silurian. 
These discoveries have cast so much doubt upon the true age 
of much of the remainder, that I have, in several cases, been 
unwilling to follow authority in calling it Archean. The work 
Archean, with much certainty, the belt of red granites running 
from Mount Desert to the Bay of Chaleur. The Archean area 
of northern New York should probably be slightly reduced ;* 
ba the age of the principal part of it seems pretty well deter- 
in 
a n and his colleagues of the Canada Survey. Prof. Selwyn 
é informs me that recent work of the Survey has shown a con- 
erase of the Huronian belt north of Lake Huron to beyond 
a. DEE. Considerable portions of the so-called Archean area 
mio pad and others, to be the equivalent of the. 
to re foe which reason they might with probability be referred 
the Silurian; but the data yet published have seemed so in- 
PO that the writer has preferred to leave the area uncol- 
une; Both this and the metamorphic area of Minnesota, as yet 
©xplored, doubtless include some genuine Archean. 
are en netamorphics of Missouri are probably Archzan, and 
80 colored. ‘Those of Arkansas and part of those of Texas 
* Brooks, this Journal, III, iv, 22. 
