covered
or partially occupied by them. This group of beds has, according to
these writers and authorities, been removed by the agencies of
denudation. The Triassic areas in New Jersey consist of slates,
sandstones (arkose), and conglomerates, with interbedded or transverse
dikes of eruptive dolerites (trap-rock), and the same order is
representative of this formation in Connecticut. These rocks in the
intermediate zone of New York presumably would have had a considerable
thickness, and the physical proportions of the process of their
complete removal would appear necessarily larger than even the great
resource the geologist possesses in long periods of time would
competently meet.
Dr.
Julien has attempted to reinforce this hypothesis by a rather untenable
suggestion. As the minerals known as zeolites, usually associated with
decomposing igneous rocks, are found sparingly on Manhattan Island, and
as their implantation on unaltered rock suggests the percolation
downward of •the currents of water charged with them, Julien has
presupposed an overlying trap rock (Triassic) from whose
decomposition they were derived. This can hardly be maintained.
Stilbite (a zeolite) was taken many feet below the bed of the East
River, and its origin could scarcely be attributed to the weathering of
overlying trap. The occurrences are also too sporadic and individual.
And Dr. Julien has himself amplified the evidence for the igneous
character of much of the island schist.
Recent
study and speculation have, however, developed a geological
reconstruction of the rock or land surfaces in the New York area, which
has also great interest and receives the endorsement of the United
States Geological Survey (New York City, Folio No. 83).
The
elevation of the continent proceeded slowly, with possibly intervals
or periods of more concentrated and urgent uplift, as at the close of
the Lower Silurian day and in Devonian and Carboniferous times; but,
always subjected anew
