Geological Reports on the State of New York. 45 



in -different parts of the same locality, that this test cannot always be 

 satisfactory. The chemical composition of a rock, producing good ce- 

 ment, should be ascertained, and similar external characters may after- 

 wards be relied on. 



" A siliceous limestone, with a little iron or manganese in its compo- 

 sition, appears best adapted for hydraulic cement. Limestone of this 

 character can be found at intervals in either of the formations mentioned ; 

 but experience is necessary to choose the proper portions, and some local- 

 ities afford an article far superior to others. 



" The formations from which this limestone has been selected, extend 

 across Monroe county from east to west ; the one through the towns of 

 Penfield, Brighton, Gates, Ogden, and Sweden ; the other through Men- 

 don, Rush, and Wheatland. At one locality in Ogden, this limestone 

 has been burned and used for cement in the locks on the Erie canal, and 

 is said to have been of good quality. The same kind of stone may be 

 found at the upper falls on the Genesee, at Rochester. The best mate- 

 rial of the kind, is on the land of Mr. Miller, in Penfield. The strata 

 are from two to four inches thick, compact and siliceous. The loca- 

 tion is near Rochester, and if it prove good and abundant, will be val- 

 uable." 



"Hydraulic cement can be obtained within five miles of the canal 

 throughout the whole extent of the fourth district. The same rocks 

 which furnish the article at Onondaga, continue to the Niagara river, 

 and a few experiments will prove that fifty or one hundred localities 

 can be found to afford good cement." 



Bvilding Stones. — There are many places in this region where 

 excellent building stone is obtained, but there is much also that 

 is bad, as appears by the following statement, the truth of which 

 we have had occasion to observe. 



"The red sandstone and the indurated marl of the same formation 

 have been used for building stone, but experience has proved what a 

 knowledge of their composition would have foretold, viz. that in Monroe 

 county, they are almost entirely unfit for any useful purpose whatever. 

 Many apparently compact blocks of this rock will, in the course of a few 

 weeks, if exposed, crumble into a loose mass. Where used in buildings, 

 it has in some cases been little affected by the weather, but in most, it 

 has been rapidly destroyed. The aqueduct at Rochester, constructed of 

 this stone, has been for years in a dilapidated state, and will soon be en- 

 tirely unfit for use. The great objection to the stone, is the presence of 

 a large proportion of aluminous matter, absorbing water and destroying 

 the stone by the same process that the hydraulic cement is removed from 

 the walls of locks. The stone used for the aqueduct now being con- 

 structed, is far superior to the sandstone, but still unfit for the purpose. 



