A
pleasant mineralogical excursion in the Borough of Richmond can be
made from the landing place at St. George by taking the trolley cars
running on the Richmond turnpike to the Clove, turning at this latter
point to the left and walking south to the Little Clove, whence an
ascent upon a winding road, leaving the former (the Little Clove) upon
the right, brings the pedestrian to a portion of Ocean Terrace.
Excavation pits and mounds overgrown with grass or herbs advertise
the location of a surface mine. This is one of the limonite ore beds of
the island. This ore has been concentrated in favorable positions,
probably depressions, and has been derived partially from the
serpentine rocks, just as along the eastern seaboard similar ore bodies
have been formed from the disseminated iron in the limestones. It
seems also that contributions of iron oxide have been made by surface
waters leaching it from the drift. Specimens of some beauty, both of
limonite and crystallized quartz, were found formerly in these
excavations. In the locality described the position might seem
anomalous at the summit of a hill, but it must be recalled that the
actual topography of the past at the same point was different. Besides
changes of level which may have taken place, the original serpentine
hills were much higher, and this summit to-day was once a zone of
concentration below surrounding slopes, while water springs laden with
iron coming from below contributed their portion of iron oxide to the
deposit. In 1887 the writer called attention to the probable origin of
the serpentine hills of Staten Island in altered hornblende and, since
in the decomposition of hornblende the iron oxide becomes more and more
concentrated, rising in some examples from eight to eighteen per cent.
(Merrill), the process of change which resulted in serpentine assisted
the creation of limonitic deposits. The wonder really is that they are
not deeper and more general.
The
ore beds in the Borough of Richmond have yielded something like 300,000
tons, partly for blast furnaces and partly to produce red ochre paint.
The clays of the island
