The Late Minnesota Survey. — Winchell. 247 
not including the Hinckley sandstone, but extending from the 
top of the Jordan sandstone to the bottom of the Dresbach 
sandstone. These friable sandstones with their accompanying 
shales and limestones, constitute the Upper Cambrian, and lie 
non-conformably on the Potsdam which was found to be a part 
of the Keweenawan. 
(2.) The geology of the Lower Silurian in the northwest 
has had a diversified history. On making a careful and detailed 
examination, both stratigraphical and paleontological, in which 
Messrs. Ulrich, Schuchert and Scofield were the chief colabor- 
ers, it was found that, wd:ile the limestones and shales should 
be, as customaril}^ included in the Trenton and Hudson River 
groups, the Galena limestone is the stratigraphic equivalent 
of the Trenton proper, and that the stratum which had speci- 
fically been known as Trenton limestone, as that at the falls of 
St. Anthony, is in a lower position and should be denominated 
Stones River [or Birdseye] and Black River limestones, the 
latter overlying. Based on the prevalent characteristic fossils 
each of these and the Trenton proper, were subdivided into 
three parts. The Hudson River formation was identified and 
divided into Utica and Richmond. In the progress of the 
Lower Silurian investigations a large number of new species 
were discovered and described. 
(3.) The extent of the Cretaceous was found to be greater 
than had been supposed. It was found on the summits of the 
granite range in northeastern jNIinnesota, known as the Giant's 
range, at points where the Alesabi iron ore is mined. It is 
known to extend nearly as far east as the falls of St. Anthony, 
occurs in Goodhue county and it probably once covered the 
Mississippi valley if not that of lake Superior, lapping over 
into Wisconsin and Illinois. 
(4.) The early Minnesota reports are the first which in 
America recognized the duality of the Ice-age, based on the 
occurrence of interglacial deposits. The measurement of the 
time involved in the recession of the falls of St. Anthony was 
the first demonstration of the recentness of the last ice epoch.'* 
The formation of glacial lakes about the ice border when the 
slope of the country was toward the ice, the origin of kames 
(now called eskers), the superglacial position of the drift while 
being transported, especially in proximity to the ice margin, 
* Dr. E Andrews, ot Chicago, had, however, reached a similar result based 
on the dunes and beaches of lake Michigan. 
