56 
GEOLOGY OF THE THIRD DISTRICT. 
It would be an easy matter to form a correct opinion of the value of this deposit from its 
superficial workings, were an equal distribution of ore to exist throughout the mass: these 
showed that the ore obtained would not pay expenses ; hut should the opinion be correct, that 
the source of all metallic deposits is below the rock in which they are found, then the nearer 
the source, the greater the probable quantity, and the upper workings would not be a good 
guide. So also by the view adopted, the materials having been derived from the rock by the 
attraction of the walls of the mass formed by the cracks or joints, or by ordinary transudation, 
the particles collecting in the fissures, and there taking or assuming those states in which we 
find them, then no correct opinion could be given, knowing nothing from other mines of an 
equal distribution of ore in any vein or deposit of the kind. Mining is and has always been a 
lottery, but a highly useful one for those who have ample means, and love the excitement 
which springs from unexpected turns of fortune, or the chances of gain from mere possibilities 
and probabilities, and who must have a vent of the kind. 
5. UTICA SLATE. 
Black Slate or Shale. Fairfield Slate of the Reports. Greywacke, or Metalliferous 
Greywacke of Eaton. 
(No. 3. Pennsylvania Survey.) 
This rock, when unaltered, is of a deep bluish black, generally fissile, exhibiting a brown¬ 
ish or dark chocolate-color by alteration or long exposure to the weather, and producing by 
decomposition a tenaceous clayey and highly favorable soil for grass, forming the best dairy 
land of the district. It is associated with thin beds of the same kind of colored impure lime¬ 
stone, which are usually found in the lower part of the mass. These beds are from one to 
five inches in thickness, the greater number of them being fitted for flagging, and of good 
quality. The slate often presents thin veins of white lamellar carbonate of lime, of a line or 
more in width. 
The Utica slate contains no fragments whatever of other rocks. It is the same material 
mineralogically, which separates the dark-colored layers of the Trenton limestone. The two 
masses were coextensive deposits in the district, the material of the Trenton limestone ceasing 
to be deposited long before the deposition of the slate ceased ; the latter often showing a 
thickness whose maximum is about two hundred and fifty feet, the whole of it resting upon 
the Trenton limestone, and upon no other rock. 
With the appearance of this rock, the greater number of the Trenton limestone fossils ceased. 
Those which are found in common to the two, are Tortoise orthis, Alternating strophomena, 
Oval lingula, Puffball favosite, Giant isotelus, Senior calymene, Dentated graptolite. This 
