444 J. H. Eaton— Relations of the Sandstone, 
Art. XLVII.—On the relations of the Sandstone, Conglomerates 
and Limestone of Sauk County, tats to each other and to 
the Azo ; by Prof. James H. Eaton 
THE age of the quartzite hills and ridges of Sauk County 
has been satisfactorily determined by Mr. Roland Irving* to 
Pre-silurian. Mr. James Hall+ in his report of the ‘State 
Survey calls them Huronian. On Dr. Lapham’s map a —_ 
region on the Eau Claire River, oeaoaine to the great centra 
area of granitic rocks, is colored as quartzite. An examina- 
tion of this locality, to determine whether ie latter rest — 
formably upon the former, would perhaps determine their age. 
For the present we can say that these rocks differ serene if 
The accompanying map is by Mr. Wm. H. Canfield, : 
Baraboo, who for many years has been the officialy surveo 
js Jpper r- 
A, Abelman; B, Baraboo; BR, Baraboo River : LN, Lower Narrows: UN . 
rows. i Devil’s Lake ; 3, g, Potsdam Sandstone; 4, Section ; 5, Limestone. ia e, 
twentieths’ of an inch equal to am ile, 
for Sauk County, and it is taken from surveys made by ee 
with the especial purpose of marking the quartzite pea : 
has been completed for Columbia County by Mr. T. C. Chan 
berlain, of Whitewater. The dotted line east of the pe 2.00 
Narrows was also added by Mr. Chamberlain. It is believ : 
that this map shows the entire outcrop of Azoic rocks in the 
region of the Baraboo River. a 
‘We have thus represented a group of islands which existe 
in the Potsdam sea, with their common trend east and west, oF 
at right angles to the dip of the rocks, 
* This Journ., Feb., 1872. + Survey of Wis., p. 11. 
