Geology and Mineralogy. 259 
With regard to the fossils of the St. Croix sandstones it is to be 
noted that their true Potsdam age has been maintained not only 
by Hall but also quite recently by Whitfield (Bulletin No. 5 of Am. 
Mus. Nat. Hist., also this Journal for April, 1884, p. 321) and 
Walcott (this Souteal, Dec., 1883, pp. 439-442); so that we have 
now the very best of paleontological authority for this reference. 
Not feeling that I possessed sufficient familiarity with the fossils of 
the Primordial prion © to justify my cyeaper ai ficoin tne ref- 
erence of those of the St. Croix sandstone to a er horizon 
than the Potsdam, I was lage es in my diseusiion of the geologi- 
cal position of the fad gta (Copper-Bearing Rocks of Lake 
Superior, pp. 442-446) to accept his statements as to this point 
for the sake of the argument. But the che since announce 
by Walcott and Whitfield, who are familiar with all the newer 
paleontological material from the earlier Caabaan horizons, as 
well as with that upon which ores pis _ conclusions twenty 
r more years since, seem to leave no m for doubt as to the 
true Potsdam age of the St. Cicix fossils. The unconformable 
position of the Keweenaw series beneath the St. Croix — 
being accepted, its pre-Potsdam age is thus rendered evident, 
I have he retofore maintained, on other than paleodtolagiaal 
ei 
grou 
the Lingulz of Taquamenon Bay, spoken of in the above 
quotation as found by Rominger, there is Aberties a misunder- 
Standing, since Rominger states distinctly that the — found 
at Taquamenon River, was found in a loose fragment o ighly 
calcareous sandstone, mixed with the drift pebbles near ot shore 
of Taquamenon Bay,” and that “the calcareous nature of this 
Specimen from Taquamenon River... .. oints to” the Calcif- 
— that, therefore, they could not have afforded the fossil-bear- 
in g, calcareous ——— found pee eae shore of the bay. 
places lyin g unconformably against the Keweenaw ama in whie 
latter position he is, as I think, undoubtedly corre 
The Taquamenon River sandstone, soe feds no argu- 
ment against the pre-Potsdam position of the Keweenaw series. 
The fossil- -bearing sandstones of the St. Prine valley furnish good 
reason for believing in “ne a ager 
Madison, Wis., January 12th, 1 
