METAMORPHIC STUDIES 359 
This cumulative extraction of salts must have an effect ultimately 
on the composition of the rocks of the shell, though perhaps so 
sight and so minutely distributed through a great mass of rocks 
that there is little hope of measuring it. 
3. Limestone.—Another cumulative segregation accompanying 
the metamorphic cycle which has come to be recognized only 
recently is the segregation of lime near the earth’s surface. As we 
follow carefully and quantitatively the anamorphic changes of all 
kinds of rocks, the fact stands out conspicuously that excess of 
lime is expelled by anamorphism. The schists and_ gneisses 
characteristic of anamorphism contain a minimum of lime car- 
bonate or even of lime silicates. To only a very limited extent lime 
enters into the constitution of platy or columnar minerals adapted 
to the anamorphic state. This expulsion of lime in anamorphism 
suggests a concentration of the lime near the surface. This is 
further suggested by another fact. It may be easily calculated 
what proportion of limestone to other sediments could be expected 
from the breaking down of igneous and crystalline rocks of average 
chemical composition, and on various calculations this has been - 
found to range from 5 to 12 per cent. It is impossible to state 
exactly the actual proportion of limestone to other sediments in 
our zone of observation, but the available facts point to a much 
higher percentage of limestone, anywhere from 25 to 50 per cent. 
It might be objected to this argument that limestones tend to 
become localized on continental areas with corresponding deficiency 
in oceanic basins, beyond our direct zone of observation. This is 
entirely possible but so far as facts are available from dredging, 
or from computations from the rate of deposition of deep-sea 
deposits, there does not seem to be this compensating deficiency. 
4. Dolomites.—Dolomites seem to be more abundant in older 
and more highly metamorphosed geological terranes than in 
later ones. As the detailed changes of the metamorphic cycle are 
followed, we find that magnesia persists through the cycle to a 
much larger extent than lime, as attested by actual analyses of 
related series of specimens. The recurrence of cycles should lead 
to an increased percentage of lime over magnesia in the great car- 
bonate formations. ‘That limestones are in larger proportion to 
