172 
IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
It is difficult to understand how eolian deposits could be dis- 
tributed continuously over so wide an area as the St. Peter 
sandstone covers. The formation is known in Minnesota, Wis- 
consin, Iowa, Illinois, and Missouri at least, and it probably 
covered originally practically the whole area of these states. 
Its extension west, south, and east from this area is not known 
accurately. The eolian theory presupposes that this whole area 
was a desert during 1 the St. Peter epoch and that deposition of 
sand was so great and so general that the underlying rock sur- 
face was buried everywhere. Sand could be so distributed by 
deposition near shore in a shallow sea, provided the shore was 
migrating toward or away from the land areas of the time. 
Such seems to have been the history of the St. Croix sandstones 
which are distributed even more widely than the St. Peter is 
known to be. 
There is no known source for such a great amount of eolian 
sand, so widely distributed. There seems to be no deposit of 
eolian sand today far from its source. The sands of the At- 
lantic Coast, of the vicinity of the Great Lakes, of Kansas and 
Nebraska, of the Great Basin, of the Sahara, can all be traced 
to a near-by source. Within the area over which the St. Peter 
is distributed, there is no possible source for the sand. The 
Prairie du Chien dolomite formation which everywhere under- 
lies the sandstone could not have furnished the sand. So far 
as is known, there was no considerable area of Cambrian sand- 
stone exposed anywhere, at the time the St. Peter was deposited. 
More likely the sand was prepared by the mature weathering 
of igneous rocks in the land area of Canada, transported by 
streams or by waves and currents to its present position, and 
then deposited in the sea. 
It is pointed out by the writer elsewhere in this volume, that 
the St. Peter sandstone lies on the irregular surface of the 
Prairie du Chien formation. The relief of this surface is more 
than 200 feet. In it are sharp, steep-walled, narrow valleys 
150 feet or more in depth. The surface seems to have been in 
maturity when the deposition of the sandstone began. Rough 
topographies, such as this, interfere with sand depositing winds, 
and it is unlikely that sand could be so laid as to fill up all 
the valleys, spread over all the divides, and bury all the hills. 
