R. Irving—Age of the Quartzites, ete. 93 
fully tested by stratigraphy. A fossil is proved, by careful 
observation, to be restricted to the rocks of a certain period 
before it is used—and then cautiously—for identifying equiva- 
lent beds. Has any one proved by careful observation that 
crystals of staurolite, cyanite, or andalusite, are restricted to 
rocks of a certain geological period? Assumptions and opin- 
ions, however strongly emphasized, are not proofs. 
It is no objection to stratigraphical evidence that it is diffi- 
cult to obtain; is very doubtful on account of the difficulties ; 
nown. Until then, lithology may give us guesses, but noth- 
ing more substantial. ; 
r. Hunt's arguments with reference to the White Mountain 
Series, as urged by him in 1870, will be found in this Journal, 
i, ; 83. Both there, and in his address, may be seen the 
n 
? 
Strata that are part of, because conformable to, these Helder erg 
beds. Had he studied up these stratigraphical relations with 
the care requisite to obtain the truth, and all the truth, perha 
he would not longer say—it is “contrary to my notions of the 
geological history of the continent to suppose that rocks of 
evonian age could in that region have assumed such litho- 
logical characters.” Notions often lead astray. 
Art. XV.—On the Age of the Quartzites, Schists, and Conglom- 
erates of Sauk County, Wisconsin ; Peat atl Irvine, M. E., 
Professor of Geology, Mining, and Metallurgy at the Univer- 
sity of Wisconsin. 
_ Turoveu the central portion of the county of Sauk, he 
west trend, and a height varying from a mere rise above the 
n th 
general prairie to an altitude of five hundred feet. The width 
from north to south never exceeds three or four miles, and in 
