60 NEW YORK STATE MUSEUM 



chiefly militate against the return of empty cars and the haulage of 

 supplies for the mines. 



Geology. As affecting the ore bodies, two geological, series are 

 of chief importance, but there are at least two others of eruptive 

 rocks which also concern them. Later than all and having little 

 to do with the ores, but mentioned so as to complete the local 

 geology, there are the Paleozoic sediments. The accompanying 

 columnar statement presents all the formations from the latest 

 above, to the oldest beneath. 



Champlain clays 



Glacial drift 

 r Utica slate 



Trenton limestone 

 Paleozoics <( Chazy limestone 



Beekmantown limestone 



Potsdam sandstone 



Diabase dikes 



Gabbros, dark, basic and more or less gneissoid. In 

 the mining localities of uncertain relation to 

 the syenites 



Augite syenites and related types more or less gneissoid 



Anorthosites more or less gneissoid 



The Grenville series of metamorphosed sediments, 



limestones, quart zites, hornblende schists and 



rusty schistose gneisses 



Champlain clays. The clays appear along the lake shore and are 



practically limited to a zone a hundred feet more or less above it. 



They have no bearing upon the iron industry. 



Glacial drift. Under this term is embraced the morainal 

 materials, sands and gravels, which beginning higher up from the 

 lake than the Champlain clays mantle all the surfaces. Even the 

 highest peaks are not free from boulders and the rounded cobbles 

 of the hard resistant Potsdam quartzite are everywhere through- 

 out the area. Sometimes the drift is water sorted but in the cases 

 which especially affect the mines in the vicinity of Mineville it 

 consists of heavy boulders and sand. In sinking the Harmony 

 shafts quite 200 feet of this overlying burden were penetrated and 

 in a neighboring bore hole, 248 feet, before bed rock was reached. 

 These depths were encountered on the side of the present valley 

 and above the stream bottom. Under these circumstances ore 

 bodies can only be located by means of a magnetic survey, and 

 this method is carried out by the companies with magnetometers 



