GEOLOGICAL HISTORY OF SERPENTINES, 175 
occurrence of serpentine, I make the following summary :—The rocks of the region, 
as is well known, belong to the Onondaga salt-group of the New York series, and occupy 
a position near the summit of the Nilurian, being overlaid by the Lower Helderberg, and 
resting upon the Niagara division. The strata are, as elsewhere throughout this region, 
undisturbed and nearly horizontal, the inclination at Syracuse, as measured by Vanuxem, 
being less than thirty feet to the mile, in a southwest direction. The thickness of the 
Onondaga salt-group is subject to great variations, and at this point, not far from its eastern 
limit, it is thinner than farther west. It is described by our author as here consisting, in 
its lower portion, of a mass of red shales, varying from 100 to 500 feet in thickness, passing 
upward into a body of greenish shales including more or less gypsum, and followed by a 
third division, in which are found masses of gypsum of economic value. 
§ 28. These occur on two horizons, one at the base and the other at the summit of the 
division, in the form of lenticular masses included in soft shales or marls, which are often 
marked by hopper-shaped cavities, doubtless formed through the removal, by solution, of 
imbedded crystals of sea-salt. Interposed in these marls is found a peculiar porous dolo- 
mite, generally drab or buff in color. The cavities in this are very irregular in form, and 
in most cases communicate with oné another. They are sometimes spherical, and contain 
spherical crusts, besides some pulverulent carbonate of lime. They also vary greatly in 
size, in some portions attaining a diameter of half an inch, and giving the rock a vesicular 
aspect. Our author remarks, “the cavities of these porous rocks have no analogy what- 
ever with those derived from organic remains,’ As seen in one locality, “the cells show 
that parts of the rock are disposed to separate into very thin layers which project into the 
cells, an effect wholly at variance with aériform cavities, but evidently the result of the 
simultaneous forming of the rock, and of soluble minerals, whose removal caused the cells 
in question ;” a condition of things which Vanuxem considers analogous to that shown by 
the hopper-shaped cavities in the associated marls. 
$ 29. The distribution of this porous dolomite in the third division of the Onondaga 
group near Syracuse is somewhat irregular. Besides a well-defined stratum extending 
over a large part of the gypsum-bearing region, and from three to four feet in thickness, 
Vauxem noticed other “masses limited in extent, without fixed positions, appearing to 
have been deposited at irregular intervals in the marls;” while in some places, as at the 
serpentine-locality about to be described, there is a lower mass, with smaller pores than 
that above, sometimes attaining a thickness.of twenty feet. The interval between 
the upper and lower gypsum-horizons, from various sections noticed by Vaunxem, would 
appear to be from forty to fifty feet. The marls found in this interval contain more or less 
disseminated gypsum, and in some cases small grains or crystalline masses of sulphur, 
and more rarely crystalline plates of specular iron in druses in the dolomite, as observed 
and shown me by Dr. Goessmann. The marls are described as yellowish or brownish in color, 
and generally soft and shaly, with harder masses included. Above this gypsiferous divi- 
sion, is a fourth, consisting of a compact magnesian limestone, marked by the presence of 
numerous small needle-shaped cavities, which forms the summit of the Onondaga group. 
§ 30. Itis, as already stated, between the two masses of porous dolomite, near Syracuse, 
that the bed of the serpentine was observed. Its thickness is not stated, but it was said 
to extend northward “for many rods.” According to the original notes of Vaunxem, there 
was seen, in ascending the hill, after passing twenty feet of the lower porous dolomite, and 
