326 Marcou’s Geology of the United States. 
do it. The progress of American geology is largely due to 
foreign geologists—to Lyell of England, and De Verneuil of 
rance; and they are honored for their labors. They were wise 
men; appreciating geological evidence, they used it cautiously 
and surely, and made each step a step of real progress. y 
did not conclude, when they came across a red sandstone, that it 
was the “ New Red” or the “Old Red;” or on the discovery of a 
magnesian limestone, that-it was the magnesian limestone of the 
Permian. They knew, with all other geologists, that mere 
color and mineral characters were the very worst test of equiva- 
lency between the rocks of the two continents; that the test will 
not answer even for the United States alone; that an appeal 
to such characters in this period of geological science betrays 
great want of experience. They came to the country expressly 
to subject all such considerations to the higher test of orgamic 
remains, and in this their great merit consists. r. Marcou, we 
et to see, has taken the course which they rejected and which 
science long since repudiated. It is true the region he examined 
was nearly destitute of fossils. But there was so much the more 
reason for doubting, as all others had done before him. 
‘1. Triassie Rocks in the Lake Superior Region. 
The only evidence that these rocks are Triassic, given by the 
author, is of the superficial kind just referred to. He has not 
claimed to find a fossil in the beds or any proof that decides the 
question. He remarks that Dr. Jackson “confirmed the justice 
of the view by finding beds with Pentamerus oblongus, an Upper 
Silurian fossil, on Keweenaw Bay. But it is known that oe 
strata of Keweenaw Point overlie the red sandstone; an 
has shown them to be Lower Silurian from the fossils — 
geological reasoning. 
The similarity of the beds and the associated trap to the Con- 
‘necticut River rocks, led early to the supposition that both migh 
be of the same age, but it was no basis for such knowledge as 
Mr. Marcou claims. Foster, Whitney, Hal], Logan, and © me 
have been over the same ground, and argue from the fossils am 
superposition that the rocks are as old as the Potsdam Sandstone. 
And yet Mr. Marcou still maintains, against all the investigations 
more recent than his own, and on evidence which geologists Kn ws 
be w 1 mrcor ea are Tra - Mr. ecsreoee 
ese geologists hold the old opinion, when on the con / 
the old one, and the only one current until the ev! 
cm: which these geologists themselv 
Gu 
