70 The American Geologist. Febiuurj, loos 
by gravitative settling or aliy other method of the more 
soluble and less quickly crystallizable part, we may have a 
coarser grain due to the practical decrease of (u) the tem- 
perature and conditions of consolidation, or the increase of 
(k) the molecular abundance of some particular mineral. 
Again at the moment of injection or effusion a certain 
width of the molten rock may crystallize, and in that case 
consolidate as though the country rock and the margin had 
the actual temperatures of injection. But within this 
stiffened rind a flow may go on before final cessation 
of motion. The consolidation just within the rind will 
be abnormally slow owing to the fresh accessions of 
heat, and when the rock finally comes to rest it will 
start with the heated rind for a country rock. Crys- 
tals of minerals except those which determine the 
stiffening of the molten, rock will be formed as it pushes 
along in and along side the rind in the belt whose tempera- 
ture is lowered to their range of formation. They will be 
the porphyritic crystals of the rhyocrystal (formed floating 
in transit) type, and may of course be swept by currents into 
the middle of the molten stream and even remelted, tending 
to lower the temperature of the stream as a whole. The 
net result of considering flowage appears to be that probably 
in considering the grain at the center a little less range of 
conditions of temperature (uo) should be assumed than for 
the margin. 
Now for some more applications. The deeper seated 
rocks, batlioliths and intrusives, are likely to have (i) hotter 
contact zones ; (2) owing to the retention of mineralizers 
under pressure, lower temperatures of consolidation, or more 
broadly conditions of consolidation more like those prevail- 
ing in the rocks in which they are injected ; (3) perhaps 
higher initial or injection temperatures; (4) broader contact 
zones. 
The zone of uniform grain is therefore probably much 
broader, and coarser grain at the margin is more likely to 
occur. If tliere is a zone of uniform grain it is likely to be 
coarser than a similar zone in an otherwise similar effusive, 
but it is not necessarily coarser than the grain of the effu- 
