HAwortu. | Ore Deposits. 123 
supplied enough to form the dolomite, and, therefore, dolo- 
mitic material must have been brought up from the under- 
lying dolomitic Silurian limestone. In the first place it 
should be remembered that no geologist has yet been able to 
account satisfactorily for the wide-spread existence of mag- 
nesia in certain limestones, so that until we are able to ac- 
count for the presence of magnesia in the Silurian limestone 
below there is a possibility that a similar origin, whenever it 
may be found, may account for the dolomite in the Joplin 
area. In the next place, apparently, they were not cognizant 
of an important fact of observation, which is that throughout 
the entire district dolomite is almost universally absent in 
the great flint areas. The Galena mines are located in the 
largest flint area in the entire southwest district and not a 
trace of dolomite has yet been found within this flint area. 
Here we have mile after mile of flint rock coming to the sur- 
face and extending downward hundreds of feet, flint rock 
which is as thoroughly fissured as any in the entire district, 
fissures which are as entirely filled with secondary chert as 
any to be found, and yet no dolomite is present. On the 
other hand, whenever we approach a limestone mass dolo- 
mite appears associated with calcite, and the mines where 
limestone is or has been the most abundant are those pro- 
ducing the most dolomite. This intimate relation of the 
dolomite to the limestone beds, and this total absence of it 
from the large flint areas should be taken into account in ex- 
plaining the origin of the dolomite. It is probable that 
enough limestone has been dissolved out and carried away 
to yield many times the required amount of magnesia for the 
production of all the dolomite in the entire southwest dis- 
trict, even though the limestone contained less than one-half 
the amount of magnesia known to exist in the Burlington 
limestone, for everywhere it contains an appreciable amount. 
(¢) The almost total absence of barite or heavy spar in the 
Galena-Joplin area is significant when studied in connection 
with the great abundance of this mineral in the eastern min- 
ing districts, where the Silurian limestones are ore bearers. 
All through the eastern districts, particularly in Morgan, 
Miller and Washington counties and intervening areas, heavy 
