SPARRY LIMESTONE. 151 



western limits, is often a coarse greywacke, but this is not always the case ; and when the finer 

 varieties of gixywackc slate lie adjacent, it is very difficult to distinguish them from each 

 other. So far as discoveries have been made, this rock contains no roofing slate : it appears 

 too tender, its surface is too uneven, and it contains too great a proportion of quartz, sulphu- 

 ret of iron, etc. to be employed for economical purposes. 



1. Sparry Limestone. 



Succeeding to the slate is the rock with the above designation, which I have employed in 

 place of Sparry limerock. This name would be as useful as it is significant, provided there 

 were not other limestones with occasionally sparry veins : as it is, it will not necessarily lead 

 to error in the field, though it might in the cabinet. 



The color of this rock is unformly grey ; it weathers unevenly, by which a rough surface 

 is formed, disclosing in its composition silex and other earthy matter. It contains, besides, 

 masses of quartz which traverse the rock in an irregular manner, and numerous veins of white 

 calcareous spar which give it a chequered appearance. It dips to the east at the line of junction 

 with the slate ; but after passing farther east, the dip is changed to southwest, where it rises 

 into moderate hills whose steepest slope is upon the east side. 



To recognize the characters of this rock, is a matter not at all difficult in the field : its 

 curiously chequered surface, formed bj' a milk-white calcareous spar branching out upon a 

 grey ground, will, it is conceived, be sufficient to create in the mind an image of the rock, 

 and to impress upon it one of its most characteristic features. This rock is sufficiently pure 

 to be used for quicklime ; and accordingljr, along the belt of country which it traverses, it is 

 often burned for that purpose. When it is sound, and can be obtained in suitable masses free 

 from flaws, it would form a handsome veined and clouded marble. I do not know that it has 

 been employed for this purpose. 



This limestone is called Transition limestone upon the geological map constructed by Prof. 

 Dewey for illustrating the geology of Berkshire county, Mass. It forms a long belt which 

 stretches through the eastern tier of townships in Rensselaer and Columbia counties, as 

 Hillsdale, Canaan, Lebanon, Berhn, Petersburgh, Hoosic, and onwards in the same range 

 through Washington county into Vermont. On the Hudson river, it appears at Barnegat, 

 where it is extensively burned into lime. Like all the rocks of the Taconic system, it extends 

 a great distance north and south, while it is comparatively narrow. As it crosses the range 

 from Petersburgh to Hoosic, the direction is disturbed, and it becomes more difficult to trace 

 clearly its progress north. About two miles east of Hoosic, the range appears nearly in the 

 direction of its former strike ; but it spreads out much wider in Bennington, Vt., than it gene- 

 rally does at the south ; though it is not impossible that the Stockbridge limestone may also 

 appear upon its eastern side, and cause some difficulty in determining the true boundaries of 

 the sparry limestone. 



A subject worthy of attention, is the period of the formation of the veins of calcareous spar. 

 From observations upon other rocks, which contain fossils, which of course are free from 



