THE 
AMERICAN GEOLOGIST 
Vol. XIII. APRIL, 1894. No. 4. 
ON A NEW HORIZON AND SOME NEW LOCALITIES 
FOR FRIABLE SANDSTONE IN WHICH THE 
GRAINS ARE ENLARGED BY SECONDARY 
DEPOSITION OF SILICA IN OPTICAL 
CONTINUITY WITH THE ORIGI- 
NAL NUCLEUS. 
By Samuel Calvin, Iowa City. 
In northeastern Iowa the last forty or fifty feet of Owen's 
Lower Magnesian limestone, as it has usually been recognized 
along the Mississippi river, contains a number of thin beds of 
sandstone and shale interstratified with the characteristic 
dolomite. The first or lowest of the sandstone beds varies 
from two to three feet in thickness. It is more constant than 
the other arenaceous beds with which it is associated, it is 
also thicker than most of them, and for these reasons it may 
probably be regarded as the equivalent in Iowa of the forma- 
tion that has been called the New Richmond sandstone by the 
geologists of Wisconsin and Minnesota. The beds between 
the layer of sandstone mentioned and the base of the inco- 
herent, massive sands of the St. Peter, may then be correlated 
with the Shakopee limestone of N. II. Wine-hell. McGee, in 
his memoir on the Pleistocene History of Northeastern Iowa. 
Eleventh Annual Report, U. S. Geol. Survey, pp. 332-333, 
unites this upper portion of Owen's Lower Magnesian lime- 
stone with the St. Peter, and in the same work proposes to 
call the great body of dolomite, lying below the horizon of the 
first intercalated sand bed, the Oneota limestone. The beds 
in question, however, seem to have more intimate relations 
with the underlying dolomite than with the St. Peter. Dolo- 
mite predominates, the thin beds of sandstones being wholly 
subordinate in importance. For probably more than ninety- 
