124 NEW YORK STATE MUSEUM 



700,000 tons in the period from 1864 to 1897 when it was closed. 

 Its operation was discontinued because of falls of rock which 

 endangered further work and which were occasioned by removal 

 of the roof and pillars in changing from underground to open pit 

 excavation. The deposit consisted of a lens 160 feet thick in the 

 middle, tapering toward either end, and over 500 feet long on the 

 300 foot level along the major axis which followed the strike of the 

 gneiss east of north. The workings had attained a depth of over 

 600 feet when production ceased. The geology of the deposit is 

 of great interest on account of the mineral associations; the mag- 

 netite while lying in gneiss contains masses of limestone and is 

 itself intermixed with such minerals as chondrodite, spinel, chlorite 

 and serpentine, which indicate contact effects from some nearby 

 igneous intrusion. The same relations hold for the Mahopac mines 

 in Putnam county and the O'Neil mine in Orange county. The 

 ore averaged about 50 per cent iron as shipped and was used for 

 Bessemer pig. The Tilly Foster Iron Co. worked the mine. 



Mahopac. The Mahopac Iron Ore Co. developed a deposit in 

 the town of Cannel i| miles north of Mahopac Falls which it 

 worked in the eighties of the last century on a considerable scale. 

 The magnetite occurs in an irregular body, described by Smock 

 as four veins or beds which coalesce into two and in places into 

 one bed. The ore was worked for a length of 450 feet and to a 

 depth of about 500 feet. An analysis of a sample of 10,000 tons 

 of the shipping ore is reported to have carried 54 per cent iron, 

 .012 phosphoms and .014 sulphur. A railroad was built to connect 

 the mines with the New York Central lines (Putnam division). 



Croft and Todd mines. These are in Sprout Brook valley, a 

 deep long trench in the gneiss area north of Peekskill, eroded 

 apparently along a belt of crystalline limestone. The walls of the 

 valley are gneiss and gneissic granite and the floor is limestone 

 which is rarely exposed on account of the heavy drift mantle. The 

 Croft mine is opened on the west side, 6 miles in a direct line from 

 Peekskill, near the base of the steep ridge which limits the valley 

 on that side. It consists of a series of pits on the outcrop and a 

 tunnel entrance started 100 feet or so below the outcrop to the 

 southeast of it near the highway. The length of the workings is 

 about 700 feet. The seam shows wavelike rolls which cause con- 

 siderable variations of thickness, but the average is about 10 to 

 12 feet. The strike is ,west of north a few degrees and the dip 

 30° to 35° east. The ore is fine grained and ranges from fairly rich 

 magnetite carrying 55 per cent or so of iron to lean ore with horn- 

 blende gangue. Pyrite is present in small amount. Smock states 



