60 NEW YORK STATE MUSEUM 



ECONOMIC PRODUCTS 



ROAD METAL 



Road metal of good quality is abundant within the borders of 

 the quadrangle. To get the best results a road metal should be 

 homogeneous, hard and possess a good binding or cementing power. 

 Among the Precambric rocks the Grenville is perhaps least valuable 

 because the rocks of that formation are mostly micaceous and the 

 presence of the slippery mica flakes in the crushed stone tends to 

 prevent a proper binding. The porphyritic granite is also not a 

 first class road metal because of the mica content. The syenite, 

 though still little used, should furnish very satisfactory road ma- 

 terial since the rock is hard, pretty homogeneous, free from mica, 

 and rich in iron minerals. The iron minerals on decomposition 

 would supply a cement. During the summer of 1910 a large quarry, 

 for State road work, was opened in the syenite along the river road 

 just north of Northville. 



By far the best rock in the whole district for road building is the 

 gabbro or diabase which occurs in the small dikes shown on the 

 map. The supply of this rock is not large but enough is available 

 to build many miles of highway. This rock, commonly called 

 '' trap rock," is black, hard, very homogeneous and very rich in 

 iron minerals. Its durability and binding power are scarcely sur- 

 passed by any other kind of road rock. 



Among the Paleozoic rocks the Potsdam sandstone and the pas- 

 sage beds of the Theresa formation are of little value as road metal 

 because of the tendency to crumble under the traffic. The Little 

 Falls dolomite, especially where freest from sand grains, is better 

 adapted for road work. A large quarry in the dolomite has been 

 opened on the George Close farm about one and one-half miles 

 east of Mayfield and on the railroad. The rock is crushed at the 

 quarry and shipped for road metal and is said to be of good quality. 

 Some of the beds here have a pink color and all of the rock is 

 very compact and homogeneous. The Trenton limestone has been 

 considerably used, especially on the State road between Amster- 

 dam and Broadalbin. A large quarry for this purpose was opened 

 in the Trenton abOut two miles south-southeast of Perth. The 

 rock gives good satisfaction except perhaps that it is too soft. 



In the State road work during 1909 glacial boulders or erratics 

 were largely used in the vicinity of Broadalbin. Although fairly 

 good results seem to be obtained with this readily available ■ ma- 



