76 JOURNAL OF THE 



length of not more than thirty miles, and a maximum 

 width of not more than five miles. 



Fortunately for the roads leading through these sand- 

 stone areas there is an abundance of a hard, black, tough, 

 fine-grained rock, known as diabase, or trap, occurring in 

 dykes which have broken through the sandstone and now 

 appear on the surface in lines of more or less rounded black 

 masses of rock running nearly north and south. These 

 dykes vary in width from a few feet to more than one hun- 

 dred feet, and are separated from one another by distances 

 varying from a few yards to two or three miles. A dozen 

 or more of these dykes are crossed by the wagon road 

 between Chapel Hill and Morrisville. Several dykes occur 

 at and near Durham, and the rock has been used upon 

 roads leading out from Durham, but unfortunately it has 

 not been crushed into small fragments, as should have been 

 done, and hence the result has not been altogether satis- 

 factory. 



There is, probably, in both these sandstone areas a suf- 

 ficient amount of trap rock to properly macadamize every 

 prominent road that crosses them, and, after this has been 

 done, to furnish a top dressing for all public roads which 

 are likely to be macadamized in the adjacent counties. 



Trap Rock in Other Areas. — Fortunately this excellent 

 road material is, in its occurrence, not limited to the sand- 

 stone regions. Dykes quite similar to tliose which abound 

 in the areas just described are also found extending across 

 the country in many of the midland and Piedmont coun- 

 ties, and also the region west of the Blue Ridge. Hereto- 

 fore this black, "nigger-head" rock, as it is frequently 

 called, has been regarded as a useless encumbrance of the 

 ground; now, in connection with the move for better roads, 

 it must be regarded as one of our most valuable rocks. 

 The city of Winston has already made extensive use of it 

 in macadamizintr its streets, with excellent results. 



