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NEW YORK STATE MUSEUM 



AVERAGE ANALYSES OF THE CLAY AND MARL, IROQUOIS PORTLAND 



CEMENT CO. Mar] Clay 



Lime (CaO) 53.5 mS 



Silica (SiOJ .4 62.5 



Alumina (A1 2 3 ) .2 20.2 



Iron Oxid (Fe 2 3 ) .2 7.5 



Magnesia (MgO) .3 1.8 



Sulfuric anhydrid (S0 3 ) 1.7 A 



Sand and gravel industry 



The sand and gravel supplies of Rochester are secured from 

 two main sources, the Pinnacle hills, which border the southern 

 and southeastern side of the city, and the Ridge. Sand is also 

 obtained in small amounts from a thin mantle strewn over the 

 intermediate territory in the village of Brighton. Some is 

 brought on the Erie canal from BushnelPs Basin. The greater 

 part comes from the pits in the Pinnacle hills. Of these, the one 

 near the Eastern Wide-waters, just beyond the city limits, in 

 the town of Brighton, and known as Cobb's hill sandpit, is 

 worked the most extensively. It is owned by William Cobb 

 and leased and worked by Thomas Lynn, of Alliance avenue. 

 More business is done at this pit than at all the others about 

 Rochester combined. The output for the fiscal year just closed 

 could not be ascertained exactly but was approximately 30,000 

 yards of sand and gravel. Of this, 8000 yards were used for 

 repairing the towpath of the Erie canal. This pit affords the 

 sharpest sand and also the greatest variety, ranging from the 

 finest molding sand through brick, paving, plaster, coarsest 

 core, to stone sand, and yields an excellent gravel for concrete. 



The various grades of material found here are arranged 

 in such a way as to exhibit all the features of cross bedding, 

 oblique layering, high inclination of beds and rapid changes 

 from one material to another, which would be expected 

 in sections of deposits formed where a swiftly flowing stream 

 debouched into deep standing water. It is probable that the 

 succession of peaks or hills which make up this range mark the 

 points of debouchure of streams which drained the ice sheet and 



