ECONOMIC GEOLOGY 207 



The Hudson River Stone Supply Company has an extensive 

 plant for quarrying and crushing granite, at Breakneck Mt, 

 north of Cold Spring. The same company operates a second 

 plant for supplying crushed limestone at Stoneco, north of New 

 Hamburg. ; 



One of the largest quarries in the state is that of P. Callanan 

 at South Bethlehem, Albany county. The Lower Helderberg 

 limestone is the rock used and it makes a good road. 



The Cauda galli grit of Albany county is used in small quanti- 

 ties locally and makes an excellent road, though it is not durable. 



At Duanesburg, near Schenectady, sandstone of the Hudson 

 river group is crushed for road metal. 



At Pert Chester, Westchester county, a coarse-grained granite 

 is quarried and is considerably used locally, but the best ma- 

 cadam roads of that district are of limestone from Tomkins Cove. 



The gray gneiss has been considerably used as a road material 

 in Westchester county. 



On Staten Island the yellow gravel is much used for road 

 making; also the diabase or trap from the Graniteville quarries, 

 which is being extensively used on a system of county roads 

 with the most satisfactory results. 



The materials used for making roads in the state vary with the 

 locality. If the traffic on the road is moderate it is generally 

 safe to use the local material, whatever its nature, unless it be 

 shale, but if there is a heavy traffic it will pay in most instances 

 to get a stone of superior quality from elsewhere. 



The requisite qualities of a road metal are hardness and tough- 

 ness. Where both these qualities are not obtainable in the same 

 stone the latter is perhaps preferable. 



Silicious rocks, though often hard, do not consolidate as well 

 nor so quickly as limestone, owing to the sandy detritus formed 

 by the former having no cohesion. The detritus of magnesian 

 limestone acts like a mortar. 



Granite and gneiss, especially if very micaceous, are apt to dis- 

 integrate rapidly and produce dust and mud. 



