HAWORTH. | Detailed Geology. 89 
the western part of Bonanza are limestone. The hill on the 
south is composed of undisturbed layers of the limestone. 
That on the north is not quite so continuous limestone, but 
here and there lesser flint areas are found, which by shaft- 
ing are proved to be as badly disturbed as the so-called open 
ground. Along the creek at present everything is flint rock 
and the worst kind of open ground known in the entire dis- 
trict. 
Second, the Central Mining Company. Another place 
where this peculiar open structure is noticeable, but where 
the ground is so nearly free from water that caving is not 
bad, is on the J. M. Cooper land operated by the Central 
Mining Company, in the east half of the southeast quarter of 
section 22, southwest of Galena. The mining here is carried 
on at a depth of from 70 to 100 feet. Part of the ground is 
comparatively firm flint rock with the usual number of frac- 
tures in it making the spaces for ore bodies. Other parts of 
it are composed almost entirely of fragments which have 
fallen together after small bodies of limestone were dissolved 
out. As one travels through underground openings here 
changes in the kind of rock become very noticeable and in- 
teresting. ‘To the west of this area is a small limestone hill, 
separating the land of the Central Mining Company from 
the Mastin land on the adjoining eighty acres. The ground 
approaching the limestone hill is very largely a mass of con- 
cretionary boulders and fragmental flint fallen together with 
the greatest of irregularity. For some reason ground water 
is not bad here, and therefore the mines are worked without 
much danger of caving. But the structural conditions are 
practically identical with those at Bonanza. 
Third, Cooper hollow. Along the upper part of Cooper 
hollow, west of the state line, the mining area is bordered 
both north and south by limestone hills, and here, as else- 
where under same conditions, the flint rock is very badly 
fractured and the ground correspondingly open. Concre- 
tionary forms are not so noticeable here as in the two places 
last named, but otherwise the structure is quite the same. 
Fourth, North Empire. Unusually rich ore beds found in 
