204 NEW YORK 8TA.TE MEJSEUM 



The stone of the drift is generally hard and durable, having 

 resisted the wear of rough transportation. The economic use of 

 the surface stones of the drift in constructive work, where they 

 can be laid up in walls, is a desirable utilization of what is still 

 in many parts of the state worse than waste — a nuisance in the 

 tilling of the soil. This formation can not, however, be con- 

 sidered as one of the important sources of stone in the quarry 

 industry, although capable of yielding a great deal of rough 

 stone. It will no doubt do so in the future clearing and improve- 

 ment of the country. 



Road Metal 



In New York the best materials for road metal are trap, granite 

 and magnesian limestone. 



Trap is a general term for some of the basic eruptive rocks, the 

 word being related to or derived from the German Treppen which 

 signifies a flight of steps and is suggested by the somewhat regu- 

 lar manner in which the rock is jointed. 



The trap which is used in New York for a road metal is a dia- 

 base and consists chiefly of the minerals augite and labradorite, 

 the former being a silicate of iron and magnesia, and the latter 

 being a lime-soda feldspar. Other minerals are present in small 

 quantity but do not influence the properties which make the rock 

 valuable as a road metal. 



While sufficiently hard to resist the wear of heavy traffic to a 

 satisfactory extent, it possesses a high degree of binding or 

 cementation power. This means that the dust produced by wear 

 when moistened unites quite firmly and forms a cement which 

 binds the larger fragments to a considerable extent. 



This property is most noticeable in rocks containing much lime, 

 magnesia and alumina. 



Good trap is found only in Richmond and Rockland counties, 

 and in the intermediate area of New Jersey bordering the Hudson 

 river. Its outcrop is known as the ' Palisades.' 



Granite consists chiefly of quartz mixed with one or more of the 

 feldspars and hornblende or a mica. Hornblende has essentially 



