THE MODE OF FORMATION OF CERTAIN GNEISSES 

 IN THE HIGHLANDS OF NEW JERSEY— Concluded 



CLARENCE N. FENNER 

 Geophysical Laboratory, Carnegie Institution of Washington 



PART II. DISCUSSION OF CERTAIN THEORETICAL PRINCIPLES 

 INVOLVED IN THE INJECTION OF THE MAGMA 



It has been pointed out that the granitic magma which was 

 intruded into the original series seems to have been of a rather thin 

 consistency. Nevertheless the degree of fluidity could hardly 

 have approached, even approximately, that of water or an ordinary 

 aqueous solution. The manner in which strata have been crumpled 

 and twisted by movements of the magma argues a very effective 

 degree of viscosity, as does also the support seen to have been 

 offered to thinly tabular sheets of strata standing in a nearly up- 

 right position and evidently free for considerable distances from 

 other support than that given by the adjacent magma. On the 

 other hand, certain phenomena indicate that magmatic fluid was 

 absorbed by the strata with little difficulty. At first sight these 

 properties appear quite inconsistent with each other; nevertheless 

 it seems possible to harmonize them. In order to derive a probable 

 explanation of this and certain other phenomena it is necessary 

 to consider certain of the properties of magmatic solutions. 



At the present time it is well recognized that the temperature 

 of fusion of the individual minerals of a rock, or even the tempera- 

 tures required to fuse the aggregate, afford no indication of the 

 temperatures at which the magma from which the rock crystallized 

 was liquid in the interior of the earth. Since the time of Elie 

 de Beaumont^ the importance of the role played by water and 

 other so-called mineralizers in lowering the temperature of fusion 

 and increasing the liquidity of magmas has been perceived; and 

 acidic magmas are regarded, for a number of reasons, as having 



' EHe de Beaumont, "Note sur les emanations volcaniques et metalliferes," Bull, 

 soc. geol.fran. (2), IV (1847), 1249-1333. 



694 



