MONROE COUNTY. 
431 
1000 tons from Messrs. Sage and Harman’s, the adjoining farm ; and 1000 tons from the 
Messrs. McVean’s farm, on lot 49. The remaining 1500 tons are supplied from an extensive 
deposit at Garbutl’s mills, on Allen’s creek. Ground plaster is sold for three dollars per ton. 
Metals. 
Iron is the only ore of any importance in this county. Blende and galena (or the sulphurets 
of lead and zinc) are found in the Niagara limestone, but never in large quantities. The 
argillaceous iron ore, already noticed, extends from the Genesee river to the eastern limits of 
the county, but has not yet been explored in any part of this distance. 
Quicklime and Hydraulic Cement. 
Quicklime is manufactured in considerable quantities from the Niagara limestone. There 
are several kilns near Rochester, and others farther west and south. East of Rochester, 
lime is made from boulders and fragments of limestone on the surface and imbedded in the 
soil. This limestone contains magnesian earth, and some other impurities, rendering the 
lime less valuable than it otherwise would be. In some localities certain strata only are used 
for making lime, and in other places the whole of the rock is too impure for that purpose. 
This is owing to the predominance of siliceous and aluminous matter. 
Hydraulic Cement. 
As this material is extensively used along the line of the Erie canal, it may be proper to 
offer some remarks on the quality and situation of the substance used for this purpose. 
Nearly all the hydraulic cement now used is brought from Onondaga. 
I have already remarked, that there is no formation to which the term hydraulic limestone 
is exclusively applicable. The upper part of the calcareous shale, as it graduates into the 
Niagara limestone, becomes, by admixture of siliceous and argillaceous matter, a substance 
considered fit for hydraulic cement. The upper portions of the gypseous rocks, by similar 
admixture, become an argillaceous limestone, used for the same purpose. 
From the circumstance that these rocks are an intermediate formation, or produced at 
the passage of a shale into a limestone, no two strata are alike. For example, an upper 
stratum may be nearly a pure limestone, while a lower one is almost wholly argillaceous ; 
thus no reliance can be placed upon its quality. The same stratum at different places may 
also change the proportion of its component parts. The greatest objection in regard to the 
stone used for this cement is, that it contains too much argillaceous matter, and for this reason 
will never withstand the action of freezing water. Much of the cement now made is of very 
inferior quality, and losses are constantly sustained from its use. This subject is one which 
requires strict and constant investigation, and the State of New-York would save large sums 
in the construction of her public works by procuring a cement of good quality. 
