SUMMARIES OF PRE-CAMBRIAN LITERATURE OF 



NORTH AMERICA FOR 1909, 1910, 191 1, AND 



PART OF 191 2 



EDWARD STEIDTMANN 

 University of Wisconsin 



II. EASTERN PART OF NORTH AMERICA 



Miss Bascom^ states that the oldest rocks of the Philadelphia 

 district are the Baltimore gneiss and the Wissahickon mica gneiss. 

 Their relation to each other is uncertain. Both are intruded by 

 granites and gabbros. 



The Baltimore gneiss presents a granitic and a gneissic phase. 

 The latter consists of alternating, fine-grained layers of mica, quartz, 

 and feldspar. The granitic variety contains quartz, feldspar, and 

 accessories of biotite, hornblende, and garnets. The alternation of 

 layers in the gneiss is regarded by Miss Bascom as evidence of 

 sedimentary origin. 



Miss Bascom believes that the Baltimore gneiss is approximately 

 of the same age as the Fordham gneiss of New York, the Stamford 

 gneiss of New England, and the Carolina gneiss of Virginia. 



' The pre-Cambrian rocks of the Trenton, N.J., district as 

 described by Miss Bascom^ consist of Baltimore gneiss and the 

 Wissahickon mica gneiss, both of which she regards as of sedimen- 

 tary origin. Besides these, there are granitic and gabbroic 

 instrusives. 



Bastin^ states that the Adirondack graphite deposits occur in 

 schists of sedimentary origin. Two types of occurrence are recog- 

 nized, one related to the dynamic metamorphism of carbonaceous 



^Philadelphia Folio, U.S. Geological Survey Folio 162, 23 pp., 12 pis., sections, 

 maps, illustrations, 1909. 



== F. Bascom et al., Trenton Folio, U.S.G.S. Folio 167, 24 pp., 4 pis., 3 figs., 1909. 



3 Edson S. Bastin, "Origin of Certain Adirondack Graphite Deposits," Econ. 

 GeoL, V, No. 2 (1910), 134-57- 



183 



