56 GEOLOGY OF THE THIRD DISTRICT. 



It would be an easy matter to form a correct opinion of tiie 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 ; but should the opinion be correct, that 

 the source of all metaUic 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, tlien 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, exliibiting 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 arc found in common to the two, are Tortoise orthis. Alternating strophomena, 

 Oval lingula, PufTball favosite, Giant isotelus. Senior calymcne, Dentated graptohte. This 



