Burbank ] 152 [Nov. 19, 



gneiss is filled with such boulders, which form a complete, but ex- 

 ceedingly rough pavement, where it is crossed by the road. The 

 masses of trap in this locality are more nearly uniform in size than 

 the granitic concretions, and are seldom more than ten or twelve 

 inches in diameter. 



So far as I observed, there were in this instance no appearances of 

 a columnar structure in the trap. This fact may be an indication 

 that what appears at the surface now was at, or near, the surface when 

 the rock was consolidated, and the concretionary structure developed 

 under slight pressure. In some other localities, especially in the river 

 valleys, trap in the form of columns of greater or less regularity may 

 be seen standing above the surface, marking the course of the dike. 

 I noticed a fine example of this kind in a dike which traverses the 

 sandstone at Haywood, Chatham Co., near the bridge across the Haw 

 River. In this case greater pressure may have given the columnar 

 form. 



The undisturbed condition of the great mass of decomposed rock, 

 which in this region covers the solid ledges, is shown by the veins 

 and dikes which retain their original positions, and in many cases pro- 

 ject above the surface, as just noticed in the case of trap dikes. The 

 graphite vein near Raleigh may be traced for a great distance along 

 the surface by the color it imparts to the soil. Granitic veins contain- 

 ing fine crystals of orthoclase and muscovite are occasionally found 

 retaining their original positions, but so far disintegrated as to allow 

 the different minerals to be easily separated. 



A small vein of this kind, which I examined carefully, appears 

 traversing the decomposed gneiss in an excavation on the Raleigh and 

 Gaston Railroad, about six miles from Raleigh. This vein extends 

 quite to the surface, but not above it, and along its course at the sur- 

 face very few fragments removed from the vein could be found. 



The granitic veins that I examined in this region were nearly all 

 of a dike-like character, and quite unlike the great " endogenous " 

 veins, which, in Massachusetts and New Hampshire, yield the fine 

 crystals of beryl, tourmaline, and other minerals. 



In their mineralogical character, in the structure and contents of 

 the veins, and in many other particulars, the rocks of this region 

 closely resemble those of northern Massachusetts east of the argillite 

 band of Worcester county. It was this resemblance that first led me 

 to make some comparative studies of the surface geology of these two 

 regions. 



