732 THOMAS LEONARD WATSON 
principal metamorphism affecting the metamorphic rocks described 
above. Greatly altered masses of porphyry are intruded into the 
surrounding schists in places, especially in Chesterfield and Lancaster 
counties." 
The granite and pegmatite are closely related in composition, and 
each is discussed in detail in the subsequent pages of this paper. 
Dikes of diabase, ranging up to 200 or more feet in width, are 
frequently noted throughout the crystalline region, where they may cut 
any of the rocks described above. ‘These vary in texture from fine- 
to moderately coarse-grained, and in composition from olivine to 
olivine-free rocks, are regarded as Mesozoic in age, and represent the 
latest intrusions in the region. 
At Hornsboro, in Chesterfield County, there is a small area of 
Juratrias sandstones penetrated by diabase dikes—an extension of 
the Wadesboro, N. C., area into South Carolina. 
The geological structure of the South Carolina crystalline region 
conforms, so far as is known, with other portions of the Atlantic 
Piedmont province. The rocks are much folded, having north- 
easterly strikes, and usually dipping at large angles either to the 
southeast or northwest. 
Very little advance has been made toward determining the age 
relations of the rocks of this region since the work of the earlier geolo- 
gists. Lieber? regarded the rocks of the King’s Mountain region as 
Silurian. Kerr? later assigned the rocks of this area to the Huronian. 
Becker+ and Nitze5 considered the rocks of the central Carolinas to 
be Algonkian. Williams® placed the surface volcanic rocks and their 
associated tuffs as pre-Cambrian. Recent work by Graton’ in the 
King’s Mountain region resulted in his assigning all the rocks of the 
region, except the diabase dikes, “ Monroe” beds, and sands of the 
coastal plain, to the pre-Cambrian. In mapping the “ Pisgah Folio” 
in North Carolina, the extreme southern portion of which includes 
tL. Cy Graton, op: cit., pps 22,123. 
2O. M. Lieber, Geological Survey of South Carolina, Vol. III, p. 149. 
3 W. C. Kerr, Geology of North Carolina, 1875, p. 133. 
4G. F. Becker, 16th Ann. Rept. U. S. Geological Survey, 1895, Part III, p. 260. 
5H. B. C. Nitze, Bull. No. 3, North Carolina Geological Survey, 1896, p. 44. 
6G. H. Williams, Journal of Geology, Vol. Il (1894), pp. 28 f. 
7L. C. Graton, op. cit., 1906, pp. 29-31. 
