SOME PRE-CAMBRIAN LITERATURE OF NORTH AMERICA 185 



which probably were developed from the metamorphism of granites, 

 and other igneous rocks and possibly some sediments. It is 

 associated with and probably intruded by the Roan gneiss, which 

 seems to have been diorite and gabbro mainly. Both the Carolina 

 and Roan gneiss are intruded by a younger, less altered granite. 



Gordon'' states that one of the major stratigraphic problems of 

 eastern North America is the separation of the pre-Cambrian from 

 the early Paleozoic sediments and the subdivision of the pre- 

 Cambrian. The problem is complicated by structural intricacy 

 and metamorphism. 



Gordon^ reports that granitic hornblende and mica gneisses, 

 quartzite, and basic eruptives of pre-Cambrian age are found within 

 the Poughkeepsie quadrangle. 



Kemp and Ruedemann^ state that the pre-Cambrian rocks of 

 the Elizabethtown and Port Henry quadrangles of the northwestern 

 part of the Adirondack region may be classified in order of age from 

 latest to the oldest as follows: (i) the unmetamorphosed basaltic 

 dikes; (2) the eruptive complex of more or less metamorphosed 

 granite, anorthosite, syenite, gabbros, and intermediate types; (3) 

 the Grenville series of limestones, ophicalcites, schists, and sedimen- 

 tary gneisses. The syenites contain lens or podlike bodies of non- 

 titaniferous magnetite with apatite. The hanging wall is generally 

 more acid than the footwall. Locally the gabbros consist domi- 

 nantly of magnetite and ilmenite. 



Kemp4 summarizes the characteristics of the pre-Cambrian of 

 New York and points out some 6i its striking similarities to the 

 pre-Cambrian of Sweden. 



The oldest pre-Cambrian rocks of the Adirondack are the 

 Grenville sedimentary gneisses and schists, intruded by bathoHths 

 of granite gneisses. These were intensely folded and then intruded 

 in the order of time by anorthosite, syenite, basic gabbros, and 



' C. E. Gordon, "Some Geologic Problems," Science, N.S., XXIX (1909), 901-3 _ 

 ^ C. E. Gordon, "Progress Report on Poughkeepsie Quadrangle," iVew York State 

 Museum Bull. 140, 1910, pp. 16-20. 



3 "Geology of the Elizabethtown and Port Henry Quadrangles," New York State 

 Museum Bull. 138, 1910, i73,pp., 21 pis., 36 figs. 



4 J. F. Kemp, "Pre-Cambrian Formations in the State of New York," Congres 

 Geologic International, 1910, pp. 699-717. 



