182 
GEOLOGY OF THE FIRST DISTRICT. 
of diluvial scratches running longitudinally. Again, thirty feet west of Third avenue, on the 
south side of Sixteenth-street, and forty feet distant from it, is another boulder, thirteen feet 
long, eight broad, seven high; it is uniform in texture like that on Sixty-third-street, in place, 
and is covered with scratches running longitudinally. Another twelve feet long, eight broad, 
and eight high, is lying in Twenty-fifth-street, about twenty rods west of Fourth avenue, 
covered with scratches in every respect like those of the last. 
Now had these boulders (which, I doubt not, have all been derived from the same rock,) 
followed strictly the course of the current indicated by the diluvial grooves on the island, they 
would have been found along the Bloomingdale road, near the Eighth avenue, and from thence 
eastward to Kipp’s bay and the Alms-house, and possibly somewhat lower down; instead of 
which, they have been carried much farther south, to Corlear’s hook, and even on Long island. 
I will here remark, that I strongly suspect that there are other localities of this rock east¬ 
ward of this island; for boulders of the same character, resembling most perfectly specimens 
of this island, have been found at West-farms, New-Rochelle, and Sawpits, which could 
scarcely have been transported from the locality on this island.* 
7. Greywacke, which is common in the valley of the Hudson. I have seen specimens 
found many years ago, in grading the streets at Corlear’s hook. These specimens closely 
resemble the rock brought to this city for the purpose of flagging the sidewalks, from Coey- 
mans and Coxsackie, also from Esopus creek; but as no specimens have come to my obser¬ 
vation recently, or since about 1830, I cannot speak from personal knowledge. 
8. Limestone, like that of the Catskill or Helderhergh mountains, abounding in Productus, 
has been found at Corlear’s hook, and in other places in the southern part of the island. I 
have a single specimen in my cabinet, obtained at that place in 1826, at the depth of forty 
feet below the natural surface. It was then a boulder two or three feet in diameter, and has 
been distributed so that but a small fragment now remains. I discovered it, and removed it 
to my cabinet, and considered it as bearing such strong evidence of its source, that I shall 
forward it to be preserved in the State Cabinet at Albany. 
9. Ferruginous sandstone, or Jasper rock, like that found in place underlying the Pali¬ 
sades, near Fort Lee. 
This rock, which is one of the most abundant next to greenstone and granite, in the south 
part of the island, I have not found north of the Harlem and Manhattanville valley. It is 
most abundant between Thirteenth and Twentieth-streets, and between Second and Fourth 
avenues. This rock, when first noticed, was supposed to be a ferruginous quartz in a state 
of disintegration; but on a closer inspection, an obscure appearance of stratification was ob¬ 
served, and the component grains were found rounded and often transparent, and cemented 
together by a large amount of oxide of iron. In some specimens it is difficult to identify 
the granular structure on account of the abundance of the cement, and the advanced stage 
of decomposition in which it is found ; in others, there is so intimate a union between the 
Vide Boulders of Westchester county. 
