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IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
able so far to determine whether it is due to wind or to waves 
and littoral currents. The deposit might be either eolian or 
marine, so far as can be determined from the stratification. 
Although it is true that the St. Peter sandstone is not highly 
fossiliferous, it does contain fossils and all of the remains are 
those of marine animals. Sardeson 2 has described thirteen 
species of pelecypods, seven species of gastropods, three species 
of cophalopods, three species of brachiopods, one doubtful 
bryozoan and one porifera. In addition the borings of marine 
worms have been found in the formation at various places. Most 
of these forms have been collected from the upper part of the 
formation, but others occur lower down. Certain it is that 
they occur in the sandstone itself. Geographically, they have 
been found at Fountain, and near St. Paul in Minnesota, and 
near Beloit, Waterloo and Baraboo in Wisconsin. Sardeson ex- 
plains the relative rarity of fossils in the formation on the 
ground that most of the shells were dissolved from the porous 
sandstone by ground water. This, explanation seems to be sat- 
isfactory. After all, the formation is little if any less fossilif- 
erous than other well-known sandstones, such as the Jordan. 
It is doubtful if there are in this country sand grains which 
owe their shape entirely to wind action. The sand dunes are 
the result of reworking marine, lacustrine, fluvial or fluvio- 
glacial sands. It cannot be known then what the shape of a 
strictly eolian sand grain is. It is possible that the St. Peter 
sandstone is eolian and yet its grains might have been shaped 
by a sea and been only slightly modified by the wind. The 
fact is that the grains of the St. Peter cannot be distinguished 
from those of the Gambian marine sandstone, under the low 
objective of the compound microscope. 
Finally the St. Peter sandstone is so nearly identical, litho- 
logically, with the marine Cambrian sandstones that it is im- 
possible to distinguish them, except by stratigraphic position 
or fossil content. The texture, textural range, and stratification 
found anywhere in the St. Peter can be duplicated in the Cam- 
brian sandstones. They seem to have had the same origin. 
It is believed, therefore, that at least the most of the St. 
Peter sandstone is marine. A sea probably covered the area 
now occupied by the formation. It seems to have advanced 
2 Sardeson F. W., Minn. Acad. Naf’l ; S'ci., Vol. IV, pp. 64-87, 1896.' 
