LIME AND CEMEN^T INDUSTRIES 759 



Sweden. The outcrops at these points generally represent the 

 beds of the upper magnesian member, and its weathered surface 

 presents a characteristic spongy appearance. 



The Magara formation presents two types of lime rock: the 

 one a dark gray, subcrystalline stone, which is used for lime and 

 building purposes, the other a gray brown, crystalline rock with 

 numerous cavities and containing a high percentage of magnesia. 



The area in which the Niagara limestone is found is more re- 

 stricted than that of most of the other limestone formations of 

 the state. The upper member of this formation is known as the 

 •Guelph limestone but is not coextensive with the lower member. 

 It forms a lenticular bed about 20 miles long and extends from 

 [Rochester westward. In the vicinity of Rochester quarries have 

 been opened in it at "New Brighton and Grates. As exposed in 

 these quarries, it is a grayish brown, finely crystalline limestone 

 -containing numbers of small cavities. The peculiar feature of 

 this rock is that it contains a large amount of magnesia and a 

 very low silica percentage, making it very adaptable for use in 

 the lining of Bessemer converters. 



Loiuer Helderherg 



This formation as formerly described includes several distinct 

 members which are known as the Tentaculite, Waterlime, Pen- 

 tamerous, lower or Catskill shaly, Becraft or upper Pentamerous, 

 and upper shaly. The formation is a widely distributed one 

 within the state and of considerable economic importance, con- 

 taining the hydraulic limestones which are extensively developed 

 at Posendale near Kingston in Ulster county. 



In his recent classification^ Dr I. M. Clarke considers the 

 Tentaculite limestone, which in this bulletin is discussed as the 

 base of the Lower Helderberg, to be the highest member of the 

 Salina. If Dr Clarke's grouping be accepted, then the most 

 westerly outcrops of the Lower Helderberg in this state are in 



^ Mem. 3, N. Y. state mus. 



