376 GEOLOGY OF THE SECOND DISTRICT. 



thing, to the Ifahan marbles. Of the locality, and of the character of the mass, whether it is 

 adapted to economical purposes, I am unable to say. If it can be procured in large sound 

 pieces, it is a very valuable material. 



Iron Ores. 



The ores of iron are confined to one species, the specular oxide. The magnetic, so far as 

 my own observation extends, does not exist in the rocks of this county. The limited extent 

 of those masses with which the iron ores are usually found, cuts otT all expectation that they 

 will ever form a very important item in the resources of this county. 



Specular Oxide of Iron. 



From the previous details of the geological structure of Jefferson, it will be seen that the 

 area in which the primary ores of iron can be expected to occur is quite limited, and that 

 they must, according to the facts and principles established by observation, be confined lo the 

 primary and the borders of the sandstone in the extreme north and northeast parts of the county. 

 This we find to be true, so far as discoveries have been made, of the mines of the specular 

 oxide in Jefferson. The following deposits only require a notice in this report. 



Iro)i Ores of Theresa. 



Within the circle of four or five miles of Theresa falls, we find several deposits of the 

 specular oxide of iron. The first which I shall notice is known as the Sliirtleff bed. It is 

 four miles east of the falls. The ore is in the primary rock. The potsdam sandstone lies 

 partially over the ore, and is deeply stained with the oxide. But the mass of ore lies below 

 the sandstone ; and though it is deeply reddened, and to the eye may appear sufficiently charged 

 with iron to ])ass for an ore of it, yet, when examined, it is found a light lean mass, the body 

 of which is wholly or mostly stone or rock. But on removing the mass of sandstone above, 

 we find a layer of ore eighteen or twenty inches thick, which rests upon an uneven floor of 

 serpentine. This is composed of the usual red oxide, without the crystalline structure which 

 is often intermixed with this ore at other places. 



This, however, is not esteemed a rich bed ; and it is barely charged with a sufficient quan- 

 tity of oxide to be received at the furnaces as lean ore, suitable to mix with the richer ores 

 in quality of a flux. It yields from fifteen to twenty per cent., or about the same per centage 

 as the ordinary bog ores. 



Serpentine is the floor upon which this ore rests, in all that part which has been laid open 

 and exposed. It is mixed with angular masses of grey quartz, giving the compound the ap- 

 pearance of a breccia. Some parts are hard and firm ; others shaly, as at the Parish veins. 



Two or three other veins, in addition to the Shirlleff mine, have been opened in the vicinity ; 

 but as they furnish only the same facts, I deem it unnecessary to give detailed descriptions of 



