HAWwoRTH. | Detailed Geology. Ue 
true that broad uplands and high hills almost invariably have 
limestones at their summits or around their borders, or it is 
found by drilling or shafting. Almost as regularly the valleys 
have an excessive amount of flint rock. And yet no general 
statement of this kind can be made without numerous ex- 
ceptions being taken. 
The limestone is usually crystalline throughout; in reality 
isa marble. Itis used to a limited extent as a building 
stone and for the manufacture of lime. It is moderately 
pure, as the following analysis will show: 
CHEMICAL COMPOSITION OF MISSISSIPPIAN LIMESTONE FROM GALENA. 
CarponatevotelimenCaCOs nnn ner 91.32 per cent. 
Carbonate of magnesia, MgCOs............... 0.80 t" 
insolubletinvacid She scrs ic ccrve ts heme qe yare 3 8.00 “e 
Inonvoxidessandraluminake “sane ne oo. 0.69 of 
BOR Ee) Des eessas' c  Ra eEA ce RNAre Ue RS 100.81 per cent. 
Mining operations have revealed many varieties of it, how- 
ever, leaving it doubtful in some instances whether the lime- 
stone observed is the primary or original rock, or whether it 
is a limestone largely worked over since ore formation began. 
Sometimes it is found coarsely crystalline, with individual 
crystals more than half an inch in diameter. Such occur- 
rences usually are associated with clay or mud-filled fissures, 
and are hard to drill and to blast, and often are spoken of by the 
miners as ‘‘bastard granite.’’ Probably all of the ‘‘granite,’’ 
so frequently mentioned by miners, is a rock of this kind; 
that is, a rock which is hard to drill because it is so tough, 
and hard to blast because it is not very brittle. 
Flint or Chert.—The flint of the mining district is a very 
interesting rock, and in some respects the most important 
one found. It has been described by so many writers that it 
would almost seem a detailed description here is unnecessary. 
And yet it is so varied in its character and mode of occurrence 
that no one’s description has been too long. There are two 
or more distinct kinds of this chert. The first is light in 
color and is generally spoken of as primary chert, because, 
evidently, it was formed before any ore formation began. 
The other is frequently spoken of as secondary chert because 
