746 THOMAS LEONARD WATSON 
alteration to’a colorless mica and kaolin. Biotite shows partial 
alteration to chlorite and iron oxide, the latter segregated in the biotite 
much after the fashion of inclusions. 
A chemical analysis of this type, given on p. 735 in Col. I, is 
noteworthy because it shows nearly equal percentages of Na,O and 
K,O and molecularly the former exceeds the latter. Calculating 
the CaO and Na,O to anorthite and albite, a plagioclase feldspar is 
obtained corresponding to Ab,An,, amounting to 33.54 per cent., 
which exceeds potash feldspar by 13.52 per cent., were all the K,O 
calculated as orthoclase. 
Fic. 4.—Bowlder outcrop of the Heath Springs coarse-grained porphyritic grant 
Three miles southwest of Heath Springs, S. C. 
The Heath Springs coarse gray granite-—This variety of granite, 
exposed in large bowlder outcrops (Fig. 4) several miles south- 
west of Heath Springs in Lancaster County, is closely similar 
mineralogically, in texture, and in color to the granite of the Wades- 
boro-Rockingham area’ to the northeast in Anson and Richmond 
counties, N. C. The granite is a porphyritic biotite granite of coarse- 
grained texture and mixed reddish- and greenish-gray color. The 
feldspars range from 1 to 25™™ in size, are highly lustrous and cleav- 
able, mostly of irregular outline, though in part flat-tabular, averaging 
about 7™™ broad by 20™™ long, twinned on the Carlsbad law, and 
partly reddish and bluish green in color. The feldspar phenocrysts 
grade into the same ground-mass constituent, thus rendering the 
porphyritic texture less pronounced, and inclose plates and shreds 
1 Journal of Geology, Vol. XII (1904), pp. 385, 386; North Carolina Geological 
Survey, 1906, Bull. No. 2, pp. 15-20. 
