Relation of the Sandstone, etc., of the Bardboo Valley. 123 



ON THE EELATION OF THE SANDSTONE, CON- 

 GLOxMEKATES AND LIMESTONE OF THE BARA- 

 BOO VALLEY TO EACH OTHER AND TO THE 

 AZOIC QUARTZITES. 



BY JAMES H. EATON, PH. D. 

 Professor of Chemistry and Mineralogy, Beloit College. 



The age of the quartzite hills and ridges of Sauk county 

 has been satisfactorily determined by Mr. Roland Irving' to 

 be pre-silurian. Mr. James Hall'^ in his report of the State 

 Survey, calls them Huronian. Their relation to the great cen- 

 tral area of azoic rocks in Wisconsin may, perhaps, be deter- 

 mined by finding their junction with the latter. On Dr. Lap- 

 ham's map a small region on the Eau Claire river, adjacent to 

 the great central area of granitic rocks, is colored as quartzite. 

 An examination of this locality, to determine whether the 

 quartzite rests unconformably upon the granite rocks, would 

 doubtless determine their age. 



The accompanying map is by Mr. Wm. H. Cantield, of 

 Baraboo, who for many years has been the official surveyor of 

 Sauk county. It is taken from surveys made by him with 

 the especial purpose of marking the quartzite outcrop. 



In regard to it I would only remark, that it does not present 

 so much the appearance of two parallel ridges, terms generally 

 used in describing the elevations on either side of the Baraboo 

 river, as of a group of islands, with a common east and west 

 trend at right angles to the dip of the rocks. These elevations 

 formed islands in the Potsdam sea. The point marked (2) on 

 the map is the locality from which the fossils were obtained, 



1 Trans, of the Wis. Acad'y, 1871-72, p. 129. 

 2 Survey of Wis., p. 11. 



