PETER SANDSTONE 
299 
Now the Carbonic sandstones in adjacent regions do not carry 
these well-rounded grains, and it is therefore believed that much 
of the Peter sandstone formerly present over the Ozark crest, 
may have been destroyed to produce the Coal Measures sandstones 
of this region. 
As the shoreline gradually shifted northward, limestone deposi¬ 
tion became dominant in the south, and the Joachim dolomite of 
Missouri and Arkansas represents, perhaps, the same horizon as 
the top of the Peter sandstone in northern regions. 
After deposition of the Peter sandstone, there seems to have 
been emergence in the Ozark region, as witnessed by the fact that 
the next formation rests on the eroded surface of the Joachim 
dolomite. Slight evidences of such erosion are seen at the top 
of the Peter sandstone farther north, but there is some reason 
to think that the emergence was greatest in the Ozark region. 
This emergence does not appear to have rejuvenated the northern 
land-mass, now worn so low that it was furnishing practically 
no sediment at all. 
With the re-advance of the sea, which seems to have come in 
very widely over the region, without a measurable time occupied 
by its spread, there suddenly appeared an abundant fauna of the 
general Lowville-Black River type, marking the base of the 
Bryant [Plattin] dolomite in Missouri and Arkansas and the 
Platteville dolomite of the Upper Mississippi Valley. If the 
Everton, Peter, and Joachim formations, and perhaps Jasper 
beds of Arkansas, be considered the Minnesotan series, then its 
deposition began earlier to the south, with considerable limestone, 
apparently before the main source of the sands, the Potsdam 
sandstones, had been uncovered at the north. With the influx 
of the added sand supply when erosion tapped this source, the 
sands encroached southward on the limestone areas, but as the 
land to the north was worn still lower, so that the supply became 
more limited, the limestone area again encroached northward 
over the sands, as at the Joachim horizon. The base of the 
Minnesotan section to the south (the Everton) is older, then, 
than any part of it in the north; while the Joachim dolomite in the 
south seems to be nearly coincident with the top of the Peter 
sandstone in the north, since both seem to rest beneath essentially 
on the same horizon. 
