Mineralogy of New York. 29 



expense. Mr. M. suggests that this bog manganese is derived 

 from the decomposition of brown spar. The deposits occupy a 

 narrow range in the vicinity of a slate rock containing this min- 

 eral ; and the spar may often be seen under its original form, 

 consisting of manganese, the result of decomposition. 



Hydraulic Limestones. — Passing by the chapters on Gypsum 

 and Marble, we cite a few of Dr. Beck's remarks on hydraulic 

 limestone. These limestones abound in the state, and, as stated 

 by Mr. Mather in 1839, six hundred thousand barrels of cement 

 were manufactured in Ulster County alone, and much of it ship- 

 ped for foreign ports. The vicinity of Chittenango affords about 

 one hundred thousand bushels annually. 



The hydraulic character of these limestones in general depends 

 on the silica, or silica and alumina or magnesia, which are inti- 

 mately mingled with the carbonate of lime in the constitution of 

 the rock. The earths are in a finely divided state, and as they 

 are disseminated uniformly through the rock, the particles are in 

 the best condition possible for an immediate combination with 

 the lime, particle to particle, to produce the silicates upon which 

 the strength of the cement depends. A common fault with or- 

 dinary mortar is that the sand is coarse, in consequence of which 

 only the exterior of the grain enters into these combinations. 

 But in the hydraulic cement the silica and lime are not only in a 

 finely divided state, but ate also intimately mingled, in a manner 

 which art could not imitate without much labor and expense. 

 The hydraulic character has been attributed also to oxyd of iron, 

 manganese, and even soda. Some or all of these substances may 

 improve its quality, but silica appears to be the most essential 

 ingredient. Dr. Beck says : 



"It appears from the experiments of Berthier and Vicat, the 

 highest authorities upon this subject, that no mixture, of which 

 silica does not form a part, acquires hydraulic properties; that 

 limes containing only silica or alumina, or better those containing 

 silica and magnesia, acquire a much greater degree of hardness 

 than the silicates of pure lime ; and that the oxides of iron and 

 manganese contribute nothing to the hardening of these bodies." 

 — p. 76. 



Prof. Beck gives the following as the composition of the hy- 

 draulic limestone of Rondout, Ulster County, before and after 

 calcination, (p. 78,) 



