IOWA ACADEMY OP SCIENCES. 
221 
In 1873 appeared the First Annual Report of the Minnesota 
Geological Survey, in which the quartzites of the southwestern 
part of the state are referred by Winchelh^ to the Potsdam of 
New York. The same authorf described the celebrated pipe- 
stone quarry and neighboring localities in southwestern Minne- 
sota in connection with a preliminary account of the geology of 
Pipestone and Rock counties. 
Irving and V an Rise, J in a paper ‘ ‘ On the Secondary Enlarge- 
ment of Mineral Fragments in Certain Rocks,” referred to a 
thin slice of the Sioux quartzite showing the quartz grains 
enlarged by the addition of secondary silicious matter. The 
quartzite rock is said to be closely interstratified with sandstone. 
It is referred to the Huronian. n 
In the first volume of the final report of the Geological Sur- 
vey of Minnesota, Winchell§ gave a full description of the 
pipestone quarry and the exposures of quartzite in Rock and 
Pipestone counties. Here again the red quartzite is regarded 
as “ probably equivalent to the New York Potsdam sandstone.” 
The account published is perhaps the fullest ever given in regard 
to the formation as represented in the southwestern portion of 
that state. 
The following year the same writer || claimed certain impres- 
sions in the pipestone of southwestern Minnesota to be of 
organic origin. A trilobite and brachipod are described and 
figured as new species. Since that time, however, considerable 
doubt has been raised as to whether or not these so-called fos- 
sils are really organic remains at all, and it has come to be 
believed generally that they are not. 
In the same report Upham'i[ published some notes on the 
geology of southeastern Dakota, in which the remarks on the 
quartzite are of importance. A number of localities are noted 
and its age referred to as Potsdam. 
About the same time Irving** issued his preliminary investi- 
gations of the Archaean formations of the northwestern states. 
The Sioux quartzite is minutely described as regards its litho- 
logical characters. Its thickness is thought to be from 3,000 
to 4,000 feet. The character of the juncture with the Cretaceous 
Geol. and, Nat. Hist. Sur. Minnesota, First Ann. Eep., p 69. Minneapolis, 1873. 
t Geol. and Nat. Hist. Sur. Minnesota, Sixth Ann. Kep., pp. 97-104. Minneapolis, 1878. 
$IJ. S. Geol. Sur., Bui. No. 8. Washington, 1881. 
§ Geol. and Nat. Hist. Sur. Minnesota, Vol. I, pp. 537-543. Minneapolis, 1884. 
II Geol. and Nat. Hist. Sur. Minnesota, Thirteenth Ann. Kep., pp. 65-92. Minneap- 
olis, 1885. 
II Geol. and Nat. Hist. Sur, Minnesota, Thirteenth Ann. Eep., pp. 88-97. Minneap- 
•olis, 1885. 
S. Geol. Sur., Fifth Ann. Eep., pp. 199-202. Washington, 1885. 
