COMPOSITION OF METAMORPHOSED SEDIMENTS 199 
fat 
The question of the value of chemical criteria is part of the 
much broader question of the extent to which transfer of materia] 
goes on in rocks during purely dynamic metamorphism. This is a 
problem of importance to geologists and one which has received 
little attention. The data at present available are of somewhat 
conflicting character. Certainly many who have worked in regions 
of metamorphic schists must have been impressed by the extent 
to which portions of the metamorphic series, originally different, 
have preserved their individuality. Dikes, though rendered 
schistose and perhaps pinched out in places, still show sharp borders 
giving no evidence of extensive interchange of material with the 
bordering rock; limestone beds in the series still show sharp borders 
after metamorphism, and original sedimentary beds may still be 
recognized as such by the development of knoten or of particular 
minerals in some of them and not in others. In rarer cases ore 
deposits have been deformed in dynamic metamorphism without 
destroying the integrity of the ore bodies or causing any migration 
of the ores into the wall rocks as in the case of the Milan, N.H., 
deposit described by Emmons. 
As the writer pointed out in his earlier paper,? many of the 
granite-gneisses of Georgia described by Dr. Watson are still 
normal granites in composition although showing marked evidence 
of dynamo-metamorphism. To quote Dr. Watsons “.... the 
granite-gneisses differ from the more massive rock phases feranite] 
simply in the marked banded or foliated structure. These are 
secondary structures induced by profound and long-continued 
dynamo-metamorphism, acting on an originally massive rock, 
similar, in mineralogical and chemical compositions, to the existing 
massive granite areas studied.”’ 
If it can be shown that important transfers of material may take 
place during dynamo-metamorphism, it still remains to be deter- 
mined whether such processes are common or exceptional in the 
tW. H. Emmons, ‘Some Ore Deposits in Maine and New Hampshire,” Bull. 
U.S. Geol. Surv., No. 432 (1910), pp. 50-60. 
2 Jour. Geol., XVII (1909), 450-51. 
3 Bull. g-a, Geol. Surv. of Georgia, p. 263. 
