The natural outcroppings of the gneiss appeared on the surface
about 16th Street, on the east side of the city, and run diagonally
across to 31st Street on 10th Avenue. North of this, much of the
surface was naked rock. It contains a large proportion of mica, a
small proportion of quartz and still less feldspar, but generally an
abundance of iron pyrites in very minute crystals, which, on
exposure, are decomposed. In consequence of these ingredients it soon
disintegrates on exposure, rendering it unfit for the purposes
of building. The erection of a great city, for which this island
furnishes a noble site, has very greatly changed its natural
condition. The geological age of the New York gneiss is undoubtedly
very old, not the Laurentian or oldest, nor the Huronian, but it
belongs to the third or White Mountain series, named by Dr. Hunt the
Montalban. It is the same range which is the basis rock of nearly all
the great cities of the Atlantic coast. It crosses New Jersey where it
is turned to clay, until it appears under Trenton, and it extends to
Philadelphia, Baltimore, Washington and Richmond, Va.
Pages:
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382