Haworts. | Geography of Lead and Zinc Ores. 53 
sediments from them may have helped to produce Coal Meas- 
ure material. 
Second, the principal elevation was subsequent to Coal 
Measure time, as vestiges of Coal Measure rocks occasionally 
found, at least as far east as Green county, Missouri, show 
that the Coal Measures extended this far to the east, and that 
during their formation the area thus covered was below sea 
level. At what particular date subsequent to Coal Measure 
time the principal elevation occurred has not yet been deter- 
mined. The total absence of Cretaceous rocks may imply 
that this area was dry land throughout Cretaceous time, or, 
it may be interpreted simply to mean that whatever Cre- 
taceous rocks were formed yielded to later erosions and were 
entirely removed. The exact date of the elevation has not 
been determined, but probably it was somewhere between 
late Coal Measure and late Tertiary time. 
Third, processes of elevation were mild, producing no great 
structural features socommon in rugged mountainous districts, 
yet sufficiently vigorous to produce occasional fractures and 
faults cutting through the Mississippian and Coal Measure 
rocks and extending to undetermined depths below. 
Fourth, All streams and drainage channels throughout the 
area are consequent upon the last uplift, as their direction is 
radial from the summit of the dome. The erosion ac- 
complished by them implies considerable age, but no more 
than might be produced since the middle or later part of 
Tertiary time. ) 
