86 EDWARD STEIDTMANN 
phosed series of rocks which vary widely in character, and include 
beds of limestone and dolomite. 
Wherry states that the pre-Cambrian rocks of Pennsylvania 
occur in three distinct belts: (1) the Catoctin belt extending south- 
west from Harrisburg into Maryland; (2) the Highland belt ex- 
tending from a point about 4o miles east of Harrisburg and crossing 
the Delaware River at Easton; (3) the Piedmont Belt which 
stretches from Philadelphia to Trenton, New Jersey. About half 
of the pre-Cambrian rocks of the Highland belt are of sedimentary 
origin. ‘The latter include crystalline limestones, quartz, mica 
schists, graphite-bearing quartzite, and amphibolitic gneiss, the 
latter being areally the most important. The principal facts on 
which belief in sedimentary origin of these rocks is based, include 
high silica and alumina content, high carbonate content, rounded 
zircons, the great longitudinal extent of the gneiss laminae, and the 
greater age of the laminae as compared with granitic intrusions of 
the region. 
1—, T. Wherry, “Pre-Cambrian Sedimentary Rocks in the Highland of Eastern 
Pennsylvania,” Geol. Soc. Am. Bull., Vol. XXTX (1918), pp. 375-92. 
[To be concluded| 
