METAMORPHIC STUDIES 355 
This change was called katamorphism by Van Hise. By 
katamorphism the rock tends to become adapted to a surface 
environment. The resulting product may be compared to a solu- 
tion, both solid and liquid, of the original rock substances and the 
atmosphere and hydrosphere. 
But there is ever present a reverse or anamorphic tendency 
which has maximum effectiveness in producing results in propor- 
tion as the substances on which it works have suffered katamor- 
phism. Its effects are conspicuous on the sediments; they are much 
less conspicuous on igneous or crystalline rocks. No sooner have 
sediments been deposited than they tend to become consolidated 
by settling and by infiltration of cements. This process of indura- 
tion is aided by the pressure of the accumulating sediments, and as 
this pressure due to burial increases, other changes take place. 
The substances which had been added in katamorphism are forced 
out: first the water; then carbon dioxide, ultimately oxygen. The 
bases are recombined with the alumina and silica to reproduce some 
of the silicates of the original rock; not all of the silicates, however, 
for certain of the bases have been carried to the sea where they 
remain in solution, and thus the original ratios of bases to alumina 
and silica cannot be reproduced without the addition of bases 
from without. The mineral molecules are on the whole more 
complex. Volume decreases by elimination of pore space, by 
elimination of substances, by new molecular groupings of higher 
density. A schistose or slaty structure is developed. Energy 
is absorbed. In proportion as the rocks are buried by the load of 
overlying sediments or in proportion as they suffer mechanical 
deformation or contact metamorphism these anamorphic changes 
are expedited. The changes tend in general to make the rocks 
. approach the igneous rocks in mineral and chemical composition. 
The succession of katamorphic and anamorphic changes above 
outlined constitutes the metamorphic cycle. It is not neces- 
sary to assume that all rocks undergo this cycle. The cycle may 
be changed to a reverse phase at any point, but the tendency is the 
same. ‘The recurrence of cycles of the type above described con- 
stitutes great earth pulsations. The movement is in one sense 
oscillatory. Van Hise has used the term ‘‘zone of katamorphism”’ 
for the region near the surface where katamorphic processes are 
