740 ` The American Naturalist. [ August, 
original substances both in form and composition. Of the authimorphic 
fragments two classes are noted, first, the authiclastic, those that have 
been unable to adapt themselves to the altered conditions and, conse- 
quently, which have been fractured, and, second, the kamptomorphic, 
embracing those fragments that have been able to adapt themselves to 
changed conditions, and so have yielded to these and have bent, or 
have assumed abnormal optical properties, such as undulous extinct- 
ions. With these terms the author describes some of the rocks studied 
and states that in many instances no traces of clastic structure remain 
in them, although they must be regarded as regionally metamorphosed 
fragmentals. Regional metamorphism, he declares, may be brought 
about by pressure alone, or by dislocation—pressure with movement 
(dynamic metamorphism). The former may act slowly, deforming the 
minerals in rocks, while the latter acts rapidly, shattering them. The 
latter process usually forms rocks like the mica-schists, with a fine 
grain, and the former coarse grained ones like the gneisses. Of course, 
the action of water, which is the agent of transportation of the new sub- 
stances added during metamorphism, may come into play in each case. 
The Verrucano rocks exhibit the effects of both kinds of regional met- 
amorphism. The article contains a great many suggestions of interest 
to students of metamorphism. 
Miscellaneous.—The conglomerates and albite schists of Hoosac 
Mountain, Mass., referred® to some time ago in these notes, have been 
described by Wolff?’ in some detail in his report on the geology of 
Hoosac Mountain. The conglomerates form gneisses which grade up- 
ward into the albite schists. Amphibolites also are described, whose 
origin is from a basic intrusive rock. A large number of photographs 
of hand specimens and thin sections of the rocks described accompany 
the paper. 
Van Hise” in the report by Irving and himself on the Penokee iron 
district, gives a number of descriptions of sedimentary and volcanic 
rocks, illustrated by a large number of plates of thin sections. The 
rocks discussed include greenstone conglomerates, crystalline schists, 
intrusive greenstones, slates, quartzites, limestones, ete. 
Ries" finds that one of the crystalline schists of the series of foliated 
rocks forming the greater portion of Westchester Co., N. Y., is a 
* American Naturalist, 1892, p. 768. 
’ Min. XXII, U.S. Geol. Survey, p. 41. 
1 Mon. XIX, U.S. Geol. Survey. 
" Trans. N. Y. Acad. Sci., Vol. XIV, p. 80. 
