Haworte. | Geography of Lead and Zine Ores. 51 
Our knowledge of detailed geology in the Indian Territory and 
Oklahoma is not sufficient to permit exact statements, but 
quite possibly this vast amount of debris was supplied in part 
from the old rocks far to the south in the Indian Territory, 
and more probably in part from the Silurian and Devonian 
rocks of the Ozark area. If this view is correct, it would 
carry the beginning of the last period of elevation backwards 
to the beginning of Coal Measure time or earlier. 
Throughout the coal-fields of northern Missouri, those in 
Randolph county particularly,” the Coal Measures themselves 
have unmistakable indications of an erosive period, implying 
an oscillatory elevation of the Ozark dome. Such features 
have not yet been discovered in the Kansas field, and possi- 
bly are not present. 
From the above indications it would seem quite probable 
that the last period of elevation of the Archean-Silurian 
rocks in Missouri began during Coal Measure time and contin- 
ued in a quiet, gradual way throughout a long period of 
geologic time. The excessive erosion in the Archean area 
likewise would imply a greater elevation, or, at least, an 
earlier one than prevailed farther westward, in the Silurian 
area. It is almost certain that the Mississippian extended 
considerably farther east than its present eastern limits, and 
that they have been worn away in a manner similar to that. 
mentioned for the Coal Measures. This is shown by the 
great thickness they have along the line of their eastern out- 
cropping. Throughout these times the drainage over the 
western part of the area was westward, and continued in 
this direction until the Rocky Mountain elevation created an 
eastern drainage, whereupon the valley between the two be- 
came occupied with Spring river and North Fork. Farther 
to the southwest Spring river merges with the Neosho and 
Grand rivers, and occupies a similar position with reference 
to the Ozark dome. This, in turn, farther south enters the 
Arkansas river, a Rocky Mountain stream, which is pushed 
suuthward by the Boston mountains, and, in turn, occupies 
the trough between the Boston uplift on the northeast and 
22. Winslow, Arthur: Mo. Geol. Surv. Rep., vol. I, p, 167, et seg. Marbut, C. F.: Mo. Geole 
Surv. Rep,, vol. XII, p. 354. 
