214 GEOLOGY. 



with metamorphic rocks of lesser age. 1 In places the gneiss is partly of sediment- 

 ary and partly of igneous origin, developed by the parallel injection of granitic 

 materials into a sedimentary series. 2 The crystalline rocks of the Highlands 

 of northern New Jersey 3 appear to be chiefly Proterozoic. They include both 

 igneous and sedimentary rocks. Among the latter are limestone (marble), 

 graphitic gneisses, and large bodies of iron ore, all of which point to the existence 

 of life at the time the beds were deposited. In the South Mountain district of 

 Pennsylvania the Proterozoic seems to be represented by igneous rocks on which 

 the Cambrian rests unconformably. In no one of the foregoing localities has 

 the Archean system been certainly identified, nor has the Proterozoic age of the 

 rocks been generally fixed with certainty. 



Similar formations in similar relations exist in the Piedmont plateau of Mary- 

 land, 4 where there is an eastern belt of crystalline rocks which are thought to be 

 Proterozoic (though perhaps including some Archean), and a western belt less 

 completely crystalline which are thought to be Paleozoic. In western North 

 Carolina 5 there is a series of meta-igneous rocks classed as Algonkian. They 

 consist of meta-diabase, epidotic and chloritic schist (probably altered basalt), 

 dark schists, and meta-rhyolites (altered from acidic glassy rocks) . All are more 

 or less metamorphic, and some of them highly so. 



Farther southeast is a great area of crystalline rocks occupying parts of Vir- 

 ginia, North and South Carolina, Georgia, and Alabama, formerly referred to the 

 Archean. In this group of rocks, strata as young as the Ordovician are known 

 to occur, though the great body of the rock is probably older. Within the group, 

 Proterozoic rocks are believed to occur, though they have not been differentiated. 

 Archean rocks have not been certainly identified. 



While the correspondence of the Proterozoic rocks in these various 

 regions with those of the Lake Superior region is not generally very 

 close, it may be pointed out again that close correspondence is not to 

 be expected, even if the rocks of different localities were contemporane- 

 ous in origin. The phases of sedimentation taking place about any 

 land mass at any time are largely dependent upon the height of the 

 land, the freeness of the exposure of its coasts, the amount of precipi- 

 tation, the climate, and the character of the formations suffering erosion. 

 These various factors were as likely to be dissimilar about the various 



^bid., p. 834, and Merrill, N. Y., folio, U. S. Geol. Surv. 



2 Van Hise, op. cit. p. 836. 



3 Wolff. See Repts. of U. S. Geol. Surv., especially those for 1893 and 1896; and 

 Wolff and Brooks, 18th Ann. Rept. TJ. S. Geol. Surv., and Bull. Geol. Soc. Am., 

 Vol. VIII, p. 397. 



4 Van Hise, op. cit.; Bascom, Md. Geol. Surv. Rept. on Cecil County, 1902. 

 This volume also gives a review of previous study, and bibliography (pp. 49-62) of 

 the literature touching this area; also Keith, Harper's Ferry, Va.-Md.-W. Va. folio 



5 Keith, Cranberry, N. C.-Tenn. folio, U. S. Geol. Surv. 



