have
disappeared through prolonged weathering, leaving the present
inconspicuous relief of the surface. This merely mechanical or local
elevation has been accomplished slowly, though even that slowness of
ascension probably was associated with periodic movements, and
it has been exaggerated or reduced by continental uplifts and
depressions. In these hills the stratified beds or their metamorphic
equivalents have been thrust up on end, or at steep angles; shearing
forces have been exerted upon them, and included igneous intrusions
have participated, along with their enclosing schists, in the folding
and plication, and there has not been wanting readjustments by faults
and dislocations.
Fossils within the limits of Greater New York are found, in place, only
in the Cretaceous beds of Staten Island (Richmond borough), though the
drift areas, in which occur transported boulders from fossiliferous
horizons in New York State, have furnished an interesting and extended
series.
METAMORPHISM
The
teachers in the schools may have some real or fancied difficulties in
understanding metamorphism. Perhaps in all its phases and in the
minutest intimacy of its mineralogical process, few or any of the
lithologists may be said to exactly understand it. It is a process of
conversion. By it mixtures of sediments containing alumina, magnesia,
lime, iron, potash, soda, boron, fluorine, phosphorus, silica in
various proportions, and generally assembled in place under the form of
clay or calcareous or arenaceous muds and sands, are changed to hard,
stony rocks with the development therein of many minerals, those so
familiar to the teachers in crystalline rocks as garnets, tourmaline,
andalusite, fibrolite, staurolites, quartz, cyanite, amphibole and
pyroxene, and many more, enclosed in mica schists, gneisses, slates,
quartzites, etc., while by it also lime muds become crystalline
limestones. It must be recalled, however, that such muds, clays, etc.,
may have had in them much crystallized material.
