248 Prof. J. W. Judd—Statical & Dynamical Metamorphism. 
perhaps of all—the rock-forming minerals, which have been subjected 
to deep-seated chemical action within the earth’s crust. 
Secondly.—The mineral (often greatly altered in its chemical 
constitution by one or other of the processes above described) may 
undergo complete transformation—either paramorphic or meta- 
chemic. Thus orthoclase, according to the nature of the solvents and 
the conditions under which they operate, may be converted wholly 
or in part into a zeolite, into muscovite or some hydrous mica, into 
epidote, into a kaolinite, or into some other type of mineral. 
It may be interesting to illustrate in a tabular form the chief 
metamorphoses to which the species orthoclase appears to be subject, 
and the complete transformations of which it is ultimately susceptible : 
A. Forms dependent upon the conditions wnder which the crystals were originally 
produced. 3 
Adularia. Sanidine. 
B. Forms resulting from physical or chemical changes, induced by statical or 
dynamical metamorphism. 
Anomalous Orthoclase Common Orthoclase. 
(Othose deformé). Opalescent Orthoclase. 
Microcline, Avanturine Orthoclase. 
Iridescent Orthoclase. 
Murchisonite. 
Perthite. 
C. New minerals resulting from the further alteration of Orthoclase. 
Zeolites. Micas. 
Epidotes, etc. Kaolinites, etc. 
Thirdly.—Statical metamorphism, by giving rise to the development 
of new minerals in a rock or to the growth of old ones, may lead to 
a complete change in the structure of a rock. Holocrystalline rocks 
are those in which the whole of the materials have acquired the crystal- 
line character without interruption, the time before their complete 
solidification having been sufficient for the prevention of any im- 
perfectly crystallized residue being left. Such rocks may be regarded 
as being in the most stable condition. But with the hypocrystalline 
rocks the case is otherwise. We have a stable portion produced by 
the uninterrupted action, up to a certain point, of crystallization, 
and an unstable portion produced during the more sudden solidifi- 
cation of the residue. In such a rock, when subjected to the process 
of statical metamorphism, the stable crystals may grow at the 
expense of their unstable surroundings, and, as I have recently 
shown, many new and remarkable rock-structures may result from 
this process.! 
It is very difficult to define any limits to the processes of statical 
metamorphism. The effects of such operations can be best studied 
in the case of igneous rocks—especially those belonging to a late 
period in the earth’s history—that have been situated near volcanic 
centres and afterwards exposed to our study through denudation. In 
such cases the phenomena which have to be investigated are less liable 
1 Quart. Journ. Geol. Soc. vol. xlv. pp. 175-186 (1889). 
