Se 
- nite mines. 
eR OC 
OF 
N APURAL SCIENC 
nS > reat)ile 
- 
Wore Vil, NO. 12. 
The regular meeting of the Association 
was held at the Staten Island Academy. 
In the absence of the president Mr. 
Samuel Henshaw was elected chairman 
pro em. : 
Messrs. Nils Bergquist, ‘Tompkinsville 
and C. A. Ingalls. Port Richmond, were 
elected active members 
The following communication was re- 
ceived from Mr. L. P. Gratacap: 
NOTES ON THE LIMONITE BEDS ON 
OCKAN TERRACE. 
Recently, in the work on the Is!and’s 
roads, a broad macadamized avenue has 
been constructed aver Ocean Terrace, 
and in the necessary re-grading of the 
old road the superficial earth was re- 
moved aud areas of soft decomposing 
serpentine exposed. This serpentine, 
saturated with water, readily crumbles in 
the hand and resembles almosta green 
clay, but hardens upon exposure to the 
air. It shows in some specimens 
a large number of included black 
specks and crystals, which are mag- 
netite, and not chromite, as far as my 
tests went. ‘This mineral may have been 
in some cases the source of the limonitic 
partings which characterize some of the 
decomposed serpentine. To quote G. P. 
Merrill] ; ‘‘under continual alternations of 
heat and cold, moisture and dryness, mag- 
netite slowly decomposes, giving rise to 
hydrated sesquioxides.”’ 
A little way to the east, and in fact 
surrounding this road at the point where 
the serpentine appears, are the old limo- 
Arse niasses, highly silice- 
SPA TEN IS 
SDINGS 
THE 
cE ASSOCIATION 
LAND: 
DECEMBER 9th, 1899. 
ous, are exposed in some of the abandoned 
excavations, These masses present sup: r- 
imposed films and crusts which indicate 
Clearly their aqueous origin There 
seems to be a necessary connection be- 
tween these limonite beds and the un- 
derlying serpentine. The former are 
clearly preglacial, the drift covering them 
completely, though along the immediate 
indefinite line of contact there is some 
intermix‘ure of drift and tron ore. The 
serpentine, weathering as do the preen 
serpentines of Harford Co., Md., into a 
“gray brown soi! whic) consists of 60 17 
per cent. silica, 10.40 per cent. of iron 
oxides, 14.81 per cent. of alumina, 
only 7.23 per cent. of magn *” would 
have furnished just the com!ipation. of 
elements requisite to 
basius of coucentration—bogs, marshes, 
or shallow lakes—the siliceous limonites, 
the pulyerulent irou soi! and the occa- 
sional magnesian carbonates—the latter, 
I believe, not fourd on Ocean Terrace— 
which are associated with the 
pentine areas on Staten Island. Iudeed 
it is not necessary 'o assume water basins. 
The meteoric waters penetrating the de- 
composing caps of serpentine would 
leave, iu time, pathered into more or less 
rich deposits, the freed iron oxide, 
assisted by a wide spread capillary action, 
constantly enriching and increasing the 
initial points of segregation. 
There seem to be no evidences of pond 
or marsh life in these limunite beds, and 
their formation may have progressed 
under sub-aérial agencies only. 
In the Gryme’s Hill ore pits streaks 
and 
esia, 
ave formed, in 
