REVIEWS 373 
heretofore been called the “western sandstone”’ (here called the Bayfield 
group) is united by Thwaites with the underlying Upper Keweenawan 
arkose sediments (here called the Oronto group) as one continuous 
formation. The results of this work show that the contact of the upper, 
or Bayfield, group with the Middle Keweenawan traps is a fault. At 
this contact there is some evidence of unconformity, but the author, 
following Van Hise and Leith, regards it as certain that the folding, 
faulting, and erosion went on during the deposition of the entire sand- 
stone series, and that the upper beds therefore overlapped with slight 
unconformity upon the older strata of the same series. The difference 
in the degree of folding of the two groups of sandstone is correlated 
with this fact. Both groups were probably deposited subaerially in a 
basin formed by the bowing of the earlier Keweenawan rocks. They 
comprise an enormous thickness of sediments, perhaps amounting to as 
much as 25,000 feet measured in the ordinary way. But the thick 
series was laid down while deformation of the region was in progress 
and thus embraces beds which overlap and shingle one another, greatly 
lessening the total bulk of the formation. 
The results of this study, while throwing much light upon the stra- 
tigraphic relations in the Lake Superior district, do not in any way 
determine the relation of the Keweenawan to the Cambrian of the Miss- 
issippi Valley. But the fact that the Bayfield group was involved in 
the profound deformation of the Keweenawan period contrasts it sharply 
with the slightly disturbed strata of the recognized Cambrian of Wis- 
consin and Minnesota. The Bayfield group as here interpreted seems, 
therefore, to be more closely allied to the Keweenawan than to the 
Cambrian. But this may be apparent rather than actual. For it is 
not unreasonable to suppose, as Van Hise and Leith have suggested in 
their Lake Superior Monograph, that subaerial sedimentation may have 
continued within this inland basin nearly or quite up to the time 
when the advancing Upper Cambrian sea entered the Lake Superior 
basin. It may therefore be that these sandstones deposited on land 
may bridge the gap between Proterozoic and Paleozoic. But until 
the relation of these sandstones to the fossiliferous beds of proven 
Cambrian age can be determined, the question of the age of the red 
sandstones still remains a debatable one. It is greatly to be hoped that 
the author will be able to carry the investigation farther in the endeavor 
to connect the Lake Superior sandstones with the fossiliferous St. Croix 
beds lying to the southwest in Minnesota, or with the Cambrian beds 
lying to the eastward in Michigan. 
ReeaAC: 
