224 ^^'^ American Geologist. -^^p"^""- ^®^i- 
such gradation. Hayes* has described an extensive porphy- 
ritic granite area near the Cartersville fault in Bartow county, 
Georgia, in which the gradation from partiahy massive to a 
highly schistose granite is plainly visible. The stratigraphic 
relations of this igneous mass, to the surrounding sedimentaries 
of known age, cannot be mistaken, and Hayes has shown the 
intrusive granite, subsequently rendered highly schistose from 
intense pressure metainorphism, to be pre-Cambrian — Archaean 
— in age. 
There appears to be, however, in most cases a sharp line of 
demarkation between the massive and slight!}- gneissoid gran- 
ites, and the extreme foliated gneisses. In many areas where 
the schistose and massive granites occur, a part of the gneisses 
are cut by true granite dikes having the same mineral and 
chemical composition, as the massive granites, which they re- 
semble in every respect. As elsewhere stated, the dikes are re- 
garded as probable apophyses from the massive type of rocks. 
If then schistose structure secondarily induced or degree of 
metamorphism be taken as an index to age relationship, in the 
case of the Georgia granitic rocks, and accepting the evidence 
so strongly pointing to igneous origin for the highly banded 
gneisses, at least two different periods of intrusion of closely 
similar acid material are represented. The query naturally fol- 
lows then whether all of these rocks have originated from the 
same parent magma ?t Chemical and mineralogical composi- 
tion more than suggest such condition. 
A very close relationship in mineral and chemical composi- 
tion is observed in the Georgia granites to similar rocks exist- 
ing to the north in the Atlantic Coast region. Kemp,$ after a 
careful study of our present knowledge of the Atlantic Coast 
granites, has emphasized the great predominance of mica- 
granites, especially the biotitic types over others ; and, with 
other investigators§ has remarked their definitely known in- 
truded character at different geological periods. Keyes^ re- 
marks in his studies of a part of the Maryland granites : "Certain 
• Hayes, C. W., Trans. Amer. Inst. Min. Engrs., Washington meeting, 
February, 190(t. 
i Kemp, J. F.. Bulletin Geol. Soc. America, 1899, vol. x, p. 382. 
J Ibid, pp. 378-382. 
§ WcLLiAMS, G. H., 15th Ann'l Rept.. V. S. G. S., 1893-94, pp. 666-670. Dr. 
Williams reviews the distribution and relative ages of igneous granites in the 
.\ppalachian Crystalliae belt and, gives numerous bibliographic references 
thereto. 
f Keves, C. R., 15th Ann'l Rept., U. S. G. S., lS93-9-i, p. 733. 
