TESTS OF ROAD MATERIAL III 



As shown by the preceding table, the New York rocks tested in the 

 laboratory of the Massachusetts Highway Commission were only sub- 

 jected to the abrasion test and therefore the results can not be fully com- 

 pared with the tests of the Massachusetts rocks which are given above. 

 Two samples of traps were tested, one from the Bouker quarry at Gutten- 

 burg and one from the quarry of Conklin & Foss at Rockland Lake. The 

 specimen tested from the Bouker quarry proved to be very much harder 

 than that from the Conklin & Foss quarry. There are two varieties of 

 trap found in the Bouker quarry ; one being considered of inferior quality 

 and known by the quarrymen as "false trap." It is part of the lower 

 portion of the trap mass and being near the sandstone which forms its lower 

 foundation, it cooled more rapidly and assumed a finer texture and a 

 harder condition than the mass above. Although this so-called false trap 

 has not been subjected to a cementation test, one would expect it to 

 prove equally valuable with the rest in this respect, as its chemical com- 

 position is probably nearly identical with that of the softer trap imme- 

 ' diately adjoining. It was a sample of the " false trap " which was tested. 



It is stated that where used at some points on Long Island it has 

 proven unsatisfactory, the fragments not holding together and forming an 

 even surface, but frequently flying out. 



The attention of the writer has been called to this fact, but he has not 

 sufficient information to warrant a full expression of opinion. The diffi- 

 culty may be due to improper construction in building the road. It 

 might also be due to the mixture of this harder variety of trap and softer 

 material from the same quarry, it being well established by experience 

 that unless the road-metal in the surface layer is of uniform hardness, 

 it will not wear uniformly. To establish the truth in this case would in- 

 volve a good deal of experimental work for which no funds are available, 

 but theorizing on the facts accessible, there seems no reason why the 

 harder trap or false trap should not make a good road provided it is kept 

 separate from material of different hardness and is laid under the super- 

 vision of a competent engineer. 



As a rule when it is not possible to make numerous tests and experi- 

 ments, it will be cheaper to use those materials which have proven satis- 

 factory in actual use. 



Owing to the press of state work it was not possible for the Massachu- 

 setts commission to make cementation tests of the specimens submitted. 

 The tests made, confirm the results of practical experience and show that 

 granite, trap and sandstone are harder and offer more resistance to abra- 

 sion than the limestones. The cementation test, when made, would un- 

 questionably show the highest cementing value to be in the limestone, 

 trap and granite and the lowest in the sandstone. 



