72 SPARRY LIMESTONE. 



speak of those points which I have inspected. On St. Albans bay, it is traversed by satin 

 spar. It is also calcareous here, as well as at numerous other points upon Lake Champlain. 

 It crops out from beneath the Calciferous sandstone at Sharpshins near Burlington. I am 

 unable to form an estimate of its thickness. 



The Taconic slate, with its subordinate beds, occupies almost the whole of Columbia, 

 Rensselaer and Washington counties. It extends to the base of the Taconic range of 

 mountains, which divides New-York from Massachusetts and Vermont. Lying in its 

 usual inclined position, if no repetitions of the same mass occur, it is of immense thick- 

 ness. For example, from Lansingburgh to the Sparry limestone in the eastern part of 

 Hoosic, near the western bounds of Bennington in Vermont, it is at least twenty miles in a 

 direct line. Its dip varies from 45° to 70°. But admitting that the same mass reappears, 

 it will still be found iuuncnsely thick. I have often examined it two miles perpendicular 

 to its strike, and found no indication of repetitions. I leave it to a future opportunity to 

 make an approximate determination of its thickness, or to others who may take up the 

 subject. 



This slate crosses the Hudson above Newburgh, and passes through Orange county into 

 New-Jersey. On the west in this latter county, we find the Hudson river shales with their 

 fossils, by which they may be distinguished from the slate. 



Without doubt this immense rock admits of subdivisions ; that is, it will probably be 

 found proper to make those masses which I have treated as subordinate, independent 

 rocks, of which perhaps others still will be recognized of sufficient importance to merit the 

 same distinction. In whatever light we may regard these minor points, there is no doubt 

 that the quantity of matter in this slate exceeds that of all the members of the New- York 

 system put together. 



§ 4. Sparry limestone. 



Distinctive characters. Origin of the Plumbaginous stale. Rock at the Western Railroad Tunnel : reappears in 

 uplifts. Resemblance to the Calciferous sandstone. Mineral contents. Range and extent. 



The name which has been retained for this mass, is acknowledged to be objectionable, 

 as most descriptive names are in geology ; for it will apply, and in fact has been applied, 

 to several different rocks. This, however, received its name from the late Prof. Eaton ; 

 and as he recognized it as a distinct rock, and I supjjose very properly, I have deemed it 

 best to retain it. 



This limestone has a bluisli ground, through which are innumerable seams of white 

 calcareous spar, which give the rock a remarkably checked appearance. Other rocks are 

 also traversed in this way, but the structure is by no means so striking. The color is 

 .sometimes a grey, varying from light to dark. It contains masses of milky as well as 

 grey hyaline quartz, which also traverse it in the form of seams. It weathers unevenly, 

 by which there is formed a rough surface impressed with fissures crossing each other in all 



