SPARRY LIMESTONE 
73 
directions. It is not a pure limestone, though it is very frequently employed for lime. 
If this rock should prove sound after it has been penetrated a few feet, it would make a 
fine and beautiful marble similar in aspect to the so-called “ Egyptian marble.” 
The dip of this rock is conformable to that of the whole system, varying from east to 
southeast. The strike corresponds also to the other members of the system, which varies 
but little in any part of its range from N. 10° E. In the State of New-York, the Sparry 
limestone occupies the belt of country comprising the eastern part of Dutchess, Columbia, 
Rensselaer and Washington counties, passing about one mile east of Hoosic four-corners ; 
and in its progress north, it strikes the west line of Arlington in Vermont. It forms the 
eastern boundary of the Taconic slate. It passes through a region of rounded hills, steeper 
upon their western than upon their eastern sides, but less elevated than the range still 
farther east, near whose bases the Stockbridge limestone ranges. It is not an easy matter 
to trace this rock continuously, partly from the great amount of debris which has been 
deposited upon it and the adjacent masses. In some parts of the range it seems to have 
been engulphed or pinched out, or lost by some of the disturbances to which the rocks 
have been subjected. Still it is a very persistent mass, and is never lost in the whole range 
through New-York but for small distances. This rock is the Transition limestone upon the 
geological map constructed by Prof. Dewey for illustrating the geology of Berkshire 
county, Massachusetts. The tunnel of the Western Railroad is cut through this rock, the 
length of which is about five hundred feet. At this place, the junction of the slate and 
limestone is by intermediate beds of plumbaginous slate, as it is termed, a variety which 
soils the fingers. 
It only requires an examination with the microscope to satisfy any one that the dark 
colored strata are highly charged with sulphuret of iron in fine crystals, which, on exposure, 
decompose and form a thin coating of a dark material, the greater portion of which is 
sulphur, mixed probably with the black oxide of iron. According to this view, there is 
no important change produced by heat at the line of contact of the rocks, but simply a 
decomposition of the sulphuret of iron disseminated through the intermediate layers. At 
the Tunnel, too, as in many other places, the limestone is highly siliceous; and so com¬ 
mon is this earth, that but few localities furnish a stone suitable for lime. I have no 
satisfactory account to give of the origin of the calcareous veins : their presence is constant, 
though not always equally profuse. 
The thick mass which I have had in view, and which ranges through the eastern part 
of the counties named, is not the only mass of limestone which possesses this character. 
Proceeding westward from this point to the western bounds of the Taconic slate, thin 
deposits of a sparry limestone occasionally occur, some of which are twenty feet thick, 
and others less; the thinnest and most unimportant being farthest towards the western 
bounds of the slate. The causes, therefore, which concurred in the production of the 
Sparry limestone, continued to operate with more or less energy, but only at intervals, 
during the whole period when the slate was being deposited. I do not suppose, however, 
that all the beds of this character are different beds: some are undoubtedly mere repeti- 
[ Agricultural Report.] 10 
