178 Editorial Comment. 
Changes of the constituent minerals with loss of identity (trans- 
formation) into isomorphic forms with unaltered chemical 
composition (paramorphism), or with composition altered 
(metachemism). 
Change of the form of the rock resulting in the development of 
granulitic or schistose structure. 
Prof. Judd remarks on the wide limits in the alteration of 
which minerals are susceptible without loss of identity, twin- 
lamellation, deformation to a system of lower symmetry (as 
orthoclase to microcline), change of the optic axial angle and 
plane, either temporary or permanent by heat and pressure, 
change of color, pleochroism and absorption, of refractive 
index, sign and intensity of double refraction, specific gravity, 
hardness and fusibility, and all these without transgressing the 
limits of specific variation. 
The eflfects of static metamorphism are then discussed. "In 
these cases the most potent agent by which change is eflected 
is the penetration of the whole mass of the rock by various 
liquid or gaseous solvents." Orthoclase is chosen as an 
example. This if formed near the surface assumes the form, 
&c. of sanidine, if at great depths those of adularia. These 
under heat and pressure can be further changed as follows : 
Original Form. 
Adularia, Sanidine, 
passes into 
Anomalous orthoclase, Common orthoclase, 
Microcline, Opalescent orthoclase, 
Avanturine orthoclase, 
Iridescent orthoclase, 
Murchisonite, 
Perthite ; 
and further into 
Zeolites, Micas, 
Epidotes,&c. Kaolinites, &c. 
Yet further in hypocrystalline rocks under the conditions of 
statical metamorphism the crystalline and stable portion may 
grow at the expense of the unstable vitreous remainder and 
many new and remarkable structures may result. 
In partial explanation of these remarkable mineral trans- 
formations in solid rock Prof. Judd cites the experiments of 
Guthrie showing that "there is a perfect gradation between the 
states of fusion and solution;" those of Spring, Van t' HoflF 
and Reicher proving that pressure can bring the molecules of 
solid bodies sufficiently close to one another to allow the action 
of chemical affinity between them which may even continue 
after the pressure is removed ; and also those of Van der Waals 
