348 The American Geologist. May. isoa 
occurrence." This is a very coinprehensivo affirmation of a hypothet- 
ical principle with which some geologists would take as broad a negative 
issue as is implied affirmatively by the author. "Percolating water" 
figures very prominently in the report, and in all the geological reason- 
ing of the author. He does not assign the origin of the crystalline 
rocks to the agents appealed to by the "crenitic hypothesis," but he 
postulates such profound changes by reason of those agents that there is 
but little choice between Wadsworth and Hunt. It is sufficient here to 
say that there is a small school of modern petrographers who explain 
many of the changes which rocks seem to have suffered, from their 
point of view — being the same changes that Dr. Wadsworth attributes 
to percolating water — by a mysterious operation named "dynamic met- 
amorphism" in which percolating water plays no part whatever. With- 
out attempting here to make peace between these contrary schools, or 
to mention any of the difficulties which obstruct the theory which Dr. 
Wadsworth adopts for the origin of the "soft ores," it is sufficient to 
say that the application of Dr. Wadsworth's views as to the origin, varia- 
tions and classification of rocks in general tends to great complexity if 
not confusion, and to make of petrology and of the geology of the 
Northwest a vast impenetrable jumble if not jungle. 
The Eastern sandstone is considered to be of the age of the Potsdam, 
of New York. It is found to underlie a small patch of Trenton lime- 
stone. This sandstone is thought most likely to be of the age of the 
Keweenaw Point traps, of the north range, there having been intermit- 
tent trap-flows during its accumulation. At least at some places the 
evidence points that way, but Dr. Wadsworth admits that in other 
places there is good evidence of a fault line along Keweenaw point, as 
claimed by Foster and Whitney, and by Irving and Charaberlin, thus 
making the Eastern sandstone of later date than the traps. This is 
also indicated by the fact that debris from the traps is found in the 
sandstone.* He suggests the very probable existence of two sandstones 
in the "Eastern sandstone," the upper one, which is seen to be first be- 
neath the Trenton would, in that case, probably represent the St. Peter 
sandstone, and the other, if later than the traps, would be the equiva- 
lent of the St. Croix sandstone of the upper Mississippi valley, which is 
known to overlie unconformably the traps at Taylor's Falls. Between 
these two is a heavy calcareous member which ought to be represented 
by some similar layer in the eastern part of the "upper peninsula," 
and which is probably that which has already furnished some few fos- 
sils in northern Michigan. 
The "south trap range" is briefly described, and is considered to be 
made up of trap-flows intersheeted with sandstone, the sandstone being 
of the age of the Eastern sandstone, the two being as conformable as 
*The subject of the age of the Eastern sandstone relatively to the 
traps was discussed at length in the American Geologist, Vol. I, p. 
44. See also Vol. Ill, p. 342, where is given the first sufficient demon- 
stration that the Cupriferous rocks are of Paleozoic age, as distin- 
guished from Mesozoic. 
