46 R. Irving—Copper-bearing Rocks of Lake Supervor. 
The statements made in the previous article, in reference to 
the zodiacal spectrum, are satisfactorily established by the re- 
sults of these observations, from which we may draw the 
following conclusion 
1. The spectrum of the zodiacal light is oe and is 
sensibly the same as that of faint sunlight or twilig 
eae right line or band can be recognized as belonging to 
this spectrum. 
3. There is no evidence of any connection between the zodi- 
acal light and the polar aurora. 
The deduction, me wn from the fact of its polarization, that 
the zodiacal light i is derived from the sun, and is reflected from 
solid matter, is thus strengthened and confirmed by the identity 
of its spectrum with that of solar light. A discussion of the 
distribution of the reflecting matter in space is reserved for 
another article. 
Yale College, June 5, 1874. 
Art. VIIL.—On the Age of the Copper-bearing Rocks of Lake Su- 
perior ; and on the Westward Continuation of the Lake Superior 
Synelinal ; by RoLanp IrRvINe. 
Durine the summer and fall of 1878, I was in charge of a 
geological teh Gon of northern Wisconsin, including the 
three counties h border on Lake Superior, on behalf of the 
State Geological Gaiver This is a region but little known, it 
- being for the most part unbroken forest, and without inhabi- 
tants except in three or four small towns immediately on the 
lake shore, the whole coast line, exclusive of islands, having 
a length not far from one hundred and twenty miles. It has 
been very little examined geologically. Portions were visited 
pool “btn by members of the various corps under Dr. D. D. 
1848-50; the easternmost of the three counties, that of 
aie. having received the most attention. Its general geo- 
logical and topographical features are very briefly described y 
Colonel Chas. Whittlesey, in the final report of Dr. Owen. 
1860, Colonel Whittlesey again visited Ashland County on 
behalf of the sag Survey of Wisconsin, then organized 
under Mr. James Hall. The results of his investigations were 
never published by the State, although some of them have ap- 
red in pamphlet form and in transactions of scientific socie- 
ties. Since that time no further examinations of the region 
have been made. 
