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181 
prison at Auburn for dwellings, stores and public edifices, the sup- 
ply being chiefly derived fronn quarries in the immediate vicinity of 
the prison. At a lower level the gray limestone appears, being a 
continuation of the strata which on Onondaga hill are quarried to 
a great extent, and noted for the beauty of their " birds-eye mar- 
ble.'^ The aqueduct at Rochester will be constructed of this lime- 
stone chiefly, and none more beautiful or durable could be found 
within the limits of our district. The same strata also occur in 
various parts of Madison county, as at the falls of Chittenango and 
Perryville, where, however, they are seldom quarried. They ter- 
minate on the east in the Helderberg mountains, where the same 
group of fossils which characterize the rocks of the Onondaga 
quarries, beautifully illustrate the identity and continuity of the 
strata. The gray limestone has a glittering appearance when 
fractured, owing to the presence of innumerable small organic re- 
lics, chiefly remains of crinoid animals, which have all been con- 
verted into spar. The organic structure is only visible on the sur- 
face of the rock which has been long exposed to the seasons. The 
form of the fossil is then distinctly visible, often in relief, which 
exhibits its minutest character, because the spar is not so readily 
acted upon by atmospheric agents as the uncrystalline portion of 
the rock. A peculiar variety of this limestone is used for orna- 
mental purposes, and termed " birds-eye marble," which is full of 
distinct annular marks of crinoidal vertebrae, looking exceedingly 
well when polished. Fine specimens of this marble may be seen 
at Syracuse, in the form of mantels and other architectural orna- 
ments. It is remarkable for its toughness, and shews indentations 
without breaking when forcibly struck with the hammer, as is ob- 
served by General Dix, in his able report to the Legislature. It 
is said not to be so readily converted into lime as the blue layers 
which alternate with it; but when free from hornstone, as is fre- 
quently the case, we infer that it would burn into a pure lime. 
Throughout this and the preceding formations, gneiss included, 
the observer will not fail to notice those remarkable parallel fis- 
sures which intersect others nearly at right angles, separating the 
rocks into regular rhomboidal masses, which greatly facilitate the 
operation of quarrying. In some localities the beautiful regularity 
of these lines give a fine eflfect to the rocks, resembling the care- 
ful joining of an artificial pavement. This is especially remarka- 
ble near Canajoharie, as seen beneath the clear water of a mill 
stream in the summer drought- 
