GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE IO9 



pany. The rock is somewhat silicious and dolomitic, as the follow- 

 ing analysis^ shows : 



Lime 29 . 07 



Magnesia 16.29 



Carbonic acid 40.76 



Alumina 2.33 



Ferric oxid -47 



Silica 10.17 



Another quarry has been opened on the west bank of the Hudson 

 in the southwestern extension of the western strip of the Wap- 

 pinger creek belt, about three-quarters of a mile south of Marl- 

 boro station. This is commonly known as Kerr's quarry. A 

 considerable enterprise was apparently projected and was in active 

 operation up to the season of 1909. During that season work was 

 suspended. 



The limestone near New Hamburg was burned for lime in earHer 

 years. Its silica and magnesia content would necessitate lean 

 returns. 



At Ruppert's quarry near Poughkeepsie the Potsdam is burned 

 for lime for private use. 



The Fishkill limestones were used for lime in earlier days, and 

 also as a flux in the operation of the Hopewell furnace a generation 

 ago. 



Limonite deposits. Limonite, or brown hematite, beds belong- 

 ing to a fairly well-defined belt of these deposits occur two miles 

 south of Fishkill Village and near Shenandoah. A small quantity 

 of ore was taken from the former in 1885. The Shenandoah mine 

 was abandoned in 1879 ^^ account of the small quantity of ore. 



The question of the origin of these deposits was discussed by 

 Professor Dana.^ According to his view, during the transition from 

 the limestone-making epoch to that of terrigenous sediments, iron- 

 bearing waters were washed into restricted basins and in the course 

 of time the calcareous and magnesian material became changed to 

 ferriferous rock. In some cases pure iron carbonate was probably 

 formed. The general magnesian character of the limestone was 

 taken as good evidence of the confined character of the basins re- 

 ceiving the additions of iron-bearing solutions. 



Kaolin. A residual deposit of kaolinite derived from the 

 disintegration of a feldspathic rock occurs near Shenandoah, and 



'N. Y. State Mus. 51st Rep't 2:434; also N. Y. State Mus. Bui. 44, p. 779. 

 2 Amer. Jour. Sci., Ser. 3. 1884. 28:398-400. 



