PRE-CAMBRIAN LITERATURE OF NORTH AMERICA 85 
intrusives listed are gabbro-amphibolite, granite gneiss, and peg- 
matite dikes. 
Miller’ gives the following classification of the pre-Cambrian 
rocks in the region of Bethlehem, Pennsylvania: 
| Franklin limestone 
Algonkian 
Vera Cruz graphitic schist 
limiterentiaied 
sneCambmien gneisses cut by dikes of basalt and 
Acid and basic igneous and sedimentary 
pegmatite 
Miller? and others describe the pre-Cambrian rocks of the 
Tolchester quadrangle east of Baltimore. The pre-Cambrian rocks 
include the acid Baltimore gneiss and the Wissahickon gneiss, both 
believed to be largely sedimentary. Their age relations are un- 
certain. These rocks are intruded by pre-Cambrian granite, gabbro, 
peridotite, and pyroxenite. 
Miller ascribes the foliation of the Grenville series of New York 
mainly to recrystallization caused by heat and pressure accompany- 
ing the upwelling of magmas, and only toa very minor degree to lat- 
eral compression. Low dips, parallelism between bedding and 
foliation, and general absence of small folds are the principal facts on 
which this view is based. ‘The foliation of the granite syenite series, 
he thinks, is an original flow and crystallization structure. The same 
view is taken of the granulated anorthosite and gabbro phases. 
Peck‘ states that the pre-Cambrian rocks of Chestnut and 
Marble hills in Northampton County, Pennsylvania, consist of a 
lower granitoid, gneissose series, overlain by a highly metamor- 
tB. L. Miller, “The Mineral Pigments of Pennsylvania,” Pennsylvania Topog. 
and Geol. Surv., Rept. No. 4 (1911), 101 pp., 29 pls., 9 figs. 
2B. L. Miller, E. B. Mathews, A. B. Bibbins, and H. P. Little, ‘‘ Description of 
the Tolchester Quadrangle, Maryland,” U.S. Geol. Surv., Geol. Ailas, Tolchester 
Folio (No. 204) (1917), 15 pp., 3 pls., maps and illus., 3 figs. 
3W. J. Miller, ‘‘Origin of Foliation in the Pre-Cambrian Rocks of Northern 
New York,” Jour. Geol., Vol. XXIV (1916), pp. 587-610, 1 fig. 
4F. B. Peck, ‘‘Preliminary Report on the Talc and Serpentine of Northampton 
County and the Portland Cement Materials of the Lehigh District, Pennsylvania,” 
Pennsylvania Topog. and Geol. Surv., Rept. No. 5 (1911), 65 pp., 17 pls. (incl. geol. 
map), 9 figs. 
