Reviews 



SUMMARIES OF RECENT NORTH AMERICAN PRE-CAMBRIAN 



LITERATURE 



C. K. LEITH 



State University, Madison, Wis. 



Edward B. Mathews. "The Structure of the Piedmont Plateau as Shown 

 in Maryland." American Journal of Science, 4th Ser., Vol. XVII (1904), 

 pp. 141-59. 



Mathews discusses the structure of the Piedmont Plateau. The Baltimore gneiss 

 (William's biotite gneiss in part) is correlated with the Fordham gneiss of New York, 

 the Arrowmink arkosic gneiss of Philadelphia, the Carolina gneiss (in part) of the 

 Washington area, all of which are referred to the pre-Cambrian. He concludes: 



1. The older rocks of the Piedmont consist of both sedimentary and igneous 

 types, which since their formation have been more or less metamorphosed. 



2. The metamorphosed sediments include banded micaceous and hornblende 

 gneisses of pre-Cambrian age; a more or less intermittent, thin-bedded, generally 

 tourmaline-bearing quartzite of Cambrian age; an intermittent dolomitic marble or 

 magnesian limestone of Cambro-Ordovician age; and a series of mica-schists and the 

 gneisses of Ordovician age. Above these occur a somewhat intermittent, poorly 

 developed quartzitic conglomerate and the Peach Bottom slates. 



3. The igneous rocks consist of an immense gabbro sheet, intruded by numerous 

 large bodies of granite and meta-rhyolite, and accompanied by numerous more basic 

 serpentinized bodies. These various masses represent stages in a single extended 

 period of igneous activity. 



4. The time when this activity took place was later than early Silurian and earlier 

 than the late Carboniferous; probably in the early part of this interval. 



5. The chief structural features of the region are the metamorphism and constant 

 schistosity, and the broader folding of the different rocks. 



6. The metamorphism of the rocks, especially of the banded gneisses, probably 

 commenced prior to the intrusion of the gabbro and granite, and was accentuated by 

 them in the eastern portion of the Plateau. 



7. The folding of the region is of the Appalachian type, the rocks occurring in 

 several long, more or less parallel, folds, with few faults and but occasional overturned 

 folds. 



8. The eastern and western areas are probably of the same age; differences in 

 metamorphism being due to the large bodies of deep-seated intrusives on the east and 

 the smaller bodies of surface volcanics on the west. 



9. The sequence found in Maryland may be recognized from Washington to 

 Trenton and in the region north of New York. 



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