a 
1895.] Petrography. 739° 
Becke’ calls attention to the frequency with which a pyroxenic ori- 
gin has been ascribed to serpentines of the Alps because of the lack in 
therm of the mesh structure, and questions the safety of this conclusion 
when based on such scanty premises. He mentions the existence of a 
serpentine in the stubachthal in the Central Alps, in the freshest por- 
tions of which olivine and picotite can be seen in large quantities, and 
in other portions diopside and olivine. In many specimens the olivine 
has been crushed into a mosaic, the finer grains of which have been 
altered into serpentine, clinochlor, antigorite and what is probably col- 
orless pyroxene. The mesh structureis found in the weathered portion 
of the antigorite-serpentine. It is thought by the author to be due to 
weathering subsequent to the production of the antigorite. 
e central mass of the east central Alps consists of granite and 
gneiss, of which the former is intrusive in the latter, although both 
have essentially the same mineralogical composition, and the former is 
schistose on its periphery. The granite contains zoisite, epidote, orthite, 
chlorite, calcite, ete., all of which are regarded as original, since the 
other primary components of the rock from which they may be assumed 
to have come are perfectly fresh. The origin of these minerals is 
ascribed to the cooling of the magma under the influence of mountain- 
making processes—a condition of crystallization which the author 
designates as piezocrystallization. The hydrated components of the 
rock are supposed to have been formed with the aid of magma moisture 
under the influence of pressure. This theory is believed to account for 
the granulation and other pressure phenomena noted in the granite, as 
well as for its composition. 
Dynamic Metamorphism.—In connection with his work on the 
rocks of the Verrucano in the Alps, Milch’ makes a study of dynamic 
metamorphism and suggests a number of terms to be used in the 
descriptions of metamorphic rocks. Allothimorphic fragments are 
those with the composition and forms of the original grains. Authi- 
morphic fragments have the forms of the grains changed but their com- 
position unchanged. Allothimorphic pseudomorphs have the original 
forms but a composition different from that of the original grains, and 
authimorphic pseudomorphs have both forms and composition changed, 
but with the latter dependent upon the original composition. Finally 
eleutheromorphic new products are those entirely independent of the 
5 Minn. u. Petrog. Mitth., XIV, 1894, p. 271. 
6 Ib., p. 717. 
7 Neues Jahrb. f. Min., etc., IX, p. 101. 
