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of the mines correlated by stratigraphy with that coal. Hence I am 
inclined to regard the plants from Henry county, Missouri, as more 
clearly contemporaneous with those in the roof of the D or ‘ Marcy’ 
coal in the northern anthracite field, though they are possibly as old 
as the C coal.” 
The reference to the unconformity at the base of the Missouri Coal 
Measures is full of significance. “‘The transgression of the water level 
during the early Mesocarboniferous time has already been discussed 
by Broadhead, Winslow, and Keyes, the state geologists. The evidence 
of the fossil plants not only corroborates their views in general, but it 
also fixes the time of the encroachment of the sea on the old coast in 
the region of Clinton. The paleobotanic criteria indicates that the 
minimum time represented by the unconformity between Jordan or 
Owen coal and the subjacent Eocarboniferous terrane is measured by 
the period required for the deposition of the Pottsville and the Clarion 
group of the Lower Productive Coal Measures, a series of rocks reach- 
ing a thickness of over 1200 feet in portions of the anthracite regions, 
and exceeding 2400 feet in southern West Virginia.” 
The depositional equivalent of the unconformity at the base of the 
Missouri Coal Measures is even more important than Mr. White has 
indicated. As quite recently stated there is farther south in Arkansas, 
a sequence of Coal Measures beneath the basal horizon of the Des 
Moines and Missourian series combined. In reality the geological 
position of the Lower Coal Measures (Des Moines series) of Missouri 
appears to be well up in the median part of the Middle Carboniferous 
instead of at the base, as generally considered. Only in Missouri, 
about one half of the Middle Carboniferous is unrepresented by strata. 
This lacking series may be represented in Arkansas by upwards of 
12,000 feet of sediments! 
Attention is called in the monograph to some of the obstacles to 
accuracy in correlation and especially to the lack of standard paleo- 
botanic sections. If ever there were opportunity of establishing a 
standard section of this kind it is in the Trans-Mississippian coal field. 
Plant remains occurs abundantly in many localities and at many hori- 
zons extending from the very base of Des Moines, up through the 
Missourian, into the so-called Permian. The monograph on the 
Missouri fossil floras considers chiefly one locality and one horizon. 
In Missouri alone there are no less than 150 known localities and 30 
horizons for coal plants. In Iowa there are nearly as many more. 
