Binal N. L. BOWEN 
distance of 3.3 m. while all the rest of the magma is unaffected, 
and similarly for the other concentration curves. 
We can, moreover, determine from the figure the amount of 
material that would be precipitated at the margin at the end of 
any period of time. At the end of infinite time the concentration 
curve would correspond with the axis of abscissae, that is, the 
concentration at all points is zero of the scale, or equal to the 
concentration of marginal saturated solution. The whole area 
a 
Re i NAS! OS 
Fic. 7.—Curves of concentration in an igneous mass showing diffusion of 
material toward a cool boundary. 
of the rectangle between the extreme ordinates of the figure repre- 
sents, therefore, on a certain arbitrary scale the amount of material 
which would be removed in bringing the whole magma to the 
concentration of the marginal saturated solution. On the same 
scale the area lying above and to the left of the concentration 
curve for any time represents the amount of material removed 
during that time. We may take a specific case and imagine that 
the mineral precipitated at the margin is, say, amphibole, which 
occurs in the magma to the extent of 20 per cent, and that the 
