THE GEOLOGICAL SECTION OF MICHIGAN 693 
conformity and erosion of the Calciferous and St. Peter’s down to the 
Lake Superior sandstone, so that at least most of the sandstone 
below the ‘‘ Trenton” limestone is Cambrian and represents the Lake 
Superior sandstone generally, or whether this sandstone represents 
the St. Peter’s sandstone, the ‘‘ Potsdam” and Calciferous having 
been overlapped, or the latter by a shoreward change of facies passed 
into a basal sandstone, which might represent continuous transgres- 
sion of the ocean. The St. Peter sandstone is well marked at the 
Wisconsin line, with a good 200 feet of Calciferous (Lower Magnesian 
dolomite) under it and also, as records just arrived show, at intervals 
along Green Bay, at least as far as Rapid River. The Calciferous 
certainly continues as a_ thick, well-marked formation well beyond 
Calciferous station and creek, and according to Rominger clear to 
T. 45 and 46 N., R. 1 W., and Neebish (Anebish) Rapids. Moreover 
a few scattered wells to rock as at Newberry in the center of the 
peninsula do not record any St. Peter’s. All these facts favor the first 
interpretation independent of the fact that it seems to fit better with 
Berkey’s interpretation of the St. Peter sandstone, though to be sure 
it implies a disconformity at Campment d’Ours Island.* 
As has been said the total thickness of this sandstone and the 
extent to which it is equivalent to the Freda and Upper Keweenawan 
sandstone are conjectural. As it laps upon the areas of older rocks 
its thickness diminishes to nothing, and there is often a conglomerate 
at its base. Its composition is largely quartz and feldspar of the acid 
varieties, sometimes up to 37 per cent. of orthoclase and microcline. 
The absence from the formation, except immediately at its contact 
with other formations, of much basic or even a large amount of 
felsitic débris which is more abundant in the Upper Keweenawan, is 
one of the reasons why we believe there can be no great discordance 
or time interval between this and the Upper Keweenawan. It seems 
to mark the culmination of the same general depression, when only 
the granite cores were exposed and finally even these were covered. 
The upper sandstone which Houghton called the “‘gray sandstone” 
he estimated at 700 feet thick. Wells indicate only some 250 feet. 
The change may indicate that the transgression had gone so far as 
practically to bury any iron-bearing rocks. 
t Cf. Rominger, Vol. I,Part 3, pp. 64, 76, 77, 82,-and 83. 
