246 Prof. J. W. Judd—Statical & Dynamical Metamorphism. 
mineral cannot change without losing its identity, the final result of 
the internal stresses set up in a rock-mass is that the constituent 
minerals are gradually transformed into totally different ones. This 
transformation may take place in two different ways sa) isi), 
paramorphic, or change into a new mineral species crystallizing in 
the same or a different system, but having the same chemical 
composition; or secondly, metachemic (to use Dana’s convenient 
term)’ when, in consequence of the addition or subtraction of 
materials, or of both of those processes combined, the chemical 
composition as well as the crystallographical characters of the 
substance undergoes complete alteration. 
Thirdly.—This change in the mineralogical constitution of a rock 
may be accompanied by a modification, more or less complete, in its 
structure. The structures which usually result from the action of 
dynamical metamorphism are the granulitic, and the foliated or 
schistose. It must be remembered that while these changes in struc- 
ture may undoubtedly take place in rock-masses which have long 
since acquired the solid condition, they are also liable to arise in 
masses which are still in a plastic or viscous condition, and as the 
result of a primary rather than of a secondary crystallization when 
the mass is under the influence of internal stresses and movements. 
I have shown how completely the granulitic structure may be 
developed on the sides of great intrusive masses of gabbro; and 
General McMahon has well illustrated the production of foliation in 
intrusive granite-veins. Hven in hypocrystalline rocks, like the 
more acid lavas, as Scrope and Darwin so admirably proved, the 
shearing movements in a slowly moving, viscous mass give rise to 
phenomena having the most striking resemblance to the foliation of 
the crystalline schists. 
Let us now direct our attention to the class of changes which take 
place in rocks which are subjected to great pressure, but in which 
this pressure has not produced differential movement resulting in 
shearing. In these cases the most potent agency by which change 
is effected consists in the penetration of the whole mass of the rock 
by various liquid or gaseous solvents. It is for the whole group of 
such changes—of which “schillerization” is a conspicuous example 
—that I propose to employ the term statical metamorphism. Such 
statical metamorphism can often be shown to have taken place in the 
same rock-masses which have undergone dynamical metamorphism 
—the statical metamorphism either preceding or following the 
dynamical metamorphism. 
The effects of statical metamorphism may be conveniently classed 
under the same three headings which we have employed in consider- 
ing the results which are produced by dynamical metamorphism. 
First.—The metamorphoses of the constituent minerals in a rock. 
We cannot perhaps better illustrate the nature and variety of the 
changes which take place in minerals subjected to great pressures 
1 Amer. Journ, Sci. (1886), vol. xxxii. p. 69-71. 
