104 NEW YORK STATE MUSEUM 



gutter at road intersections unless some person were detailed to keep it in 

 continuous repair. As this has not yet been found practicable on public 

 roads, the gutter bridge is everywhere in use, and in the spring it is a 

 fruitful source of injury to the road. It will be seen from every day obser- 

 vation and from the details stated above that the earth road while as yet 

 all that the people have agreed to have in New York has necessarily 

 many elements of self-destruction and can never be regarded as permanent. 

 The development of the wheel scraper or road machine has made it 

 possible however to keep an earth road in good condition if intelligently 

 used. 



For speedways and pleasure driving in general, a well kept earth road 

 in dry weather is superior to all others. The perfect Macadam or Tel- 

 ford road is too hard to permit of very fast driving without injury to the 

 feet of horses. 



Road Materials and their Distribution 



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 regular manner in which 

 the rock is jointed. 



The trap which is used in New York for a road metal is a diabase 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 cementing 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 consid- 

 erable extent. 



This property is most noticeable in rocks containing much lime, mag- 

 nesia and alumina. 



Good trap is known only in Richmond and Rockland counties, and in 

 the intermediate area of New Jersey bordering the Hudson river. Its 

 very prominent 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 the same composi- 

 tion as augite which occurs in trap ; and a hornblende granite should be a 



