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[ASSEMBLT 
rock formations in most parts of our country are more or less covered 
by a mantle of this deposit, of variable thickness. 
The erratic blocks of Suffolk county, and the facts relative to their ge- 
neral distribution, were alluded to in my first report. These blocks are 
the only wall stones and building stones on Long Island and the contigu- 
ous islands, with ihe exception of a small tract of gneiss in places near 
Hurlgate. The boulders and erratic blocks are found on the surface, 
and embedded in a series of strata forming the range of hills which ex- 
tend through Staten, Long, Plum, and Fisher's islands. The boulders 
on Long Island are rarely found south of the hills, but on the north 
they are observed, both embedded and on the surface, extending to the 
north shore. The varieties of rock forming the boulders in Suffolk 
county, were mentioned in the first annual report to be exactly similar, 
in all their characters, to rocks of granite, gneiss, mica, slate, hornblendic 
rocks, scienite, greenstone, serpentine rocks, verd antique, red and gray 
sandstones, &c. which occur in place in a northward direction from the 
localities where they are now found. It has also been observed, that the 
general direction of these boulders form beds of similar rock in place, 
does not coincide with the line of bearing of the strata, or the direction 
of the hills. In Queens and Kings counties, the same general facts are 
observed. Granitic and gneissoid rocks predominate on the hills and 
shore, from Oyster Bay to Little-Neck Bay, and thence to Brooklyn 
greenstone rocks are most abundant. The various rocks occurring on 
Long Island as erratic blocks, are much used for fences, wall stones in 
wells, cellars, and basements of buildings. They are nearly indestruc- 
tible by atmospheric agents, and will therefore be very durable. The 
sea wall at Sands' Point is built of fragments of the boulders found in 
the immediate vicinity. 
Some of the erratic blocks are of great magnitude. Hundreds of them 
have been seen that w^ould weigh 50 tons each. Kidd's Rock has al- 
ready been mentioned as a large erratic block, the fragments of which 
cover an area of 10 to 15 square rods, and weigh at least 2,000 tons. 
A large block was seen, half a mile to a mile S. S. E. frrm the churches 
in Plandome, called Millstone Rock, and from an observation of its cu- 
bic contents, it was estimated to weigh 1,800 tons. 
Some blocks of limestone, weighing from one to five tons each, were 
seen on the beach of Kidd's Island, half a mile from Sands' Point, which 
are precisely similar in mineralogical characters to the range of limestone 
extending from Barnegat to Pine Plains, in Dutchess county. 
