110 University Geological Survey of Kansas. 
ner remarkably similar to the ore itself, so that a description 
of the occurrence of one virtually is a description of the other. 
Likewise, the two are as intimately mixed as though they 
originated at the same time. In such cases the masses of 
secondary flint become ore and are sent to the mills in large 
quantities for crushing. Usually secondary flint is more 
abundant in large flint areas than in the border areas between 
flint and limestone. As aresult the so-called ‘‘open ground”’ 
of the miner has but little secondary flint in it, and ore 
occurring in such places is generally of high quality because 
siliceous matter is not mixed with it to any considerable ex- 
tent. Ore from the open ground, therefore, is easily milled, 
and hand picking can be carried to a great extent. In the 
early days of mining such localities were sought after so that 
the miner could sort the ore from the rock boulders and pre- 
pare the ore for market with a minimum of labor. But when 
large steam crushers and steam mills became common then 
this character of ground and of ore was no longer specially 
popular. 
It usually happens that the richest ore bodies are found in 
open ground, and likewise such ore bodies are most uncer- 
tain. The most remarkable showing of zinc ore the writer 
ever saw was in the Ashland-Wilkes mine at Belleville. 
Here when development was just beginning a face of ore was 
exposed about twenty feet high by fifty feet in length, which 
seemed rich enough to be more than half ore. Yet, at a 
later date, it was found that this wonderful showing was ex- 
ceedingly limited in extent, so that mining operations were 
carried beyond the rich ore and into ground where almost 
no ore existed. Zinc ore in open ground frequently occurs 
in individual crystals producing the so called ‘‘ pebble ore.”’ 
Klsewhere it is so finely divided and so intimately mixed 
with secondary flint that crushing must be carried to a high 
degree of perfection in order to separate the little particles of 
ore from the gangue. Open ground ore, therefore, is more 
easily milled than ore from larger flint bodies where secon- 
dary flint is so abundant. 
Here and there throughout the mining district openings 
of various sizes are found that are locally known as mud 
