2i8 THOMAS L. WATSON 



black color. When broken at an angle to the direction of the pencils, 

 the rock surface appears spotted with rounded, irregular black 

 points, ranging in size up to a half inch in diameter. At times 

 the roundish points are somewhat irregular and only partially devel- 

 oped, as shown in the lower left half of Fig. i. These may be 

 crowded close together over the surface, as seen in the figure, or 

 or they may be entirely absent from some areas and irregularly 

 distributed at wide intervals over others, as indicated in Fig. 3. 

 Indeed, the black points are reported to fail entirely in the rock 

 as the dike is traced northward, when the rock assumes a uniformly 

 light color throughout. However, every outcrop and specimen of 

 the rock seen by me contained them. 



A section cut parallel to the direction of the pencils presents a 

 surface streaked with long, somewhat irregular, though roughly 

 parallel, black lines, more or less perfect dendritic or fern-like forms 

 (Figs. 2 and 3). I was shown recently a large slab of the rock col- 

 lected from one of the outcrops since my examination in the summer 

 of 1903, which, for perfection and delicacy of tracery in fern-like 

 forms, was beautiful beyond description. The black streaks or pen- 

 cils which characterize the rock are composed of a staining of the 

 oxides of manganese and iron. 



The rock is cryptocrystalline in texture, breaking with a con- 

 chodial fracture, and is intensely hard and tough. Minute quartz 

 crystals of doubly terminated pyramidal faces are distributed through 

 the rock at irregular wide intervals. These are nowhere abundant in 

 the rock, but they are always present to some extent, and consist both 

 of the light-colored and the dark, smoky, vitreous quartz. Indeed, 

 unless carefully examined, the rock would ordinarily be pronounced 

 non-porphyritic in texture, so small and scattering are the porphy- 

 ritically developed quartzes. Megascopically, porphyritic texture 

 is nowhere particularly emphasized in the rock, but its slight develop- 

 ment is best seen on a weathered surface of the stone, where the 

 unaltered quartz crystals, though few in number and widely scat- 

 tered, contrast more strongly with the weathered surface and appear 

 more conspicuous than in the fresh rock^ Feldspars are also porphy- 

 ritically developed, as described below, though the phenocrysts are 

 difficult of differentiation in hand specimens of the rock. 



