"
stadium " consisted in the formation of specular iron, arago-nite,
calcite, which " indicate the presence of steam or heated waters and
gradually cooling waters in a new set of fissures." (Geology of Old
Hampshire County, Massachusetts, Benjamin Kendall Emerson, Monographs,
U. S. Geol. Survey, Vol. xxix.)
In
the metamorphism of the Manhattan beds there was, first, consolidation
of sediments, formation of minerals; second, disturbance, slight
pressure, and development of more minerals, and the granitic veinlets,
lenses, or the so-called pegmatized gneisses; third, mountain-making
movements, uplifts, crushing folds, etc., and slow protusion of
granite dikes and, of course, more heat and more minerals.
This
topic may be instructively dwelt upon a little longer. Metamorphism
involves (1) a change in physical condition, as from soft to harder
rocks, as from shales to flinty horn-stone, uncrystallized to
crystallized rocks, as from limestone to marble; and (2) a change in
mineralogical aggregates, as when andalusite is developed in slate,
garnet, tremolite, tourmaline, in limestone, tourmaline and quartz in
schists.
The
eruptive rocks which have invaded limestones in the Tyrol (Monzoni,
Predazzo) have developed a series of adventitious minerals, as garnet,
idocrase, spinel, anorthite, mica, apatite, magnetite, etc. Some of
these occur, however, only in the eruptive masses. There has been here
a reaction between the invaded and invading rock masses, and
a, so to speak, dry precipitation of new mineral bodies, sometimes
meaning a rearrangement of the chemical elements, or a rearrangement
with additions of new chemical elements. In the fossiliferous
zones of the Christiania district of S. Norway the eruptive granitic
rocks have produced horny, flinty rocks from the limestones and shales;
cement stone is changed to garnet; sandy layers have become quartzites;
non-calcareous clay slates are altered into chiastolitic schists; biotite mica has been developed in the limestone—and yet the fossils are not completely obliterated.
