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PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



The second specimen was like the first, porous, and slightly yellowish 

 in color, but it was softer — a circumstance due to the fact that it had 

 been lately quarried. Its composition was as follows : 



The composition of this rock indicates therefore that it might be ad- 

 vantageously employed as a fertilizing material. Although the per- 

 centage of phosphoric acid is less than in the best Carolina phosphate, 

 there is no lime to be neutralized by sulphuric acid before liberating the 

 phosphoric acid. I am informed that the extent of the deposit which is 

 represented by these analyses is very large. But the investigation of 

 the value of this material as a fertilizer would of necessity involve 

 further analyses and a more extensive investigation of this aspect of the 

 question than interests us in our consideration of the substance as a 

 building material. 



The microscopic structure of this rock indicates that it is composed 

 largely of angular grains of sand which are cemented together by a 

 fibrous material which is probably the phosphate, and by a simple re- 

 fracting substance which appears to be a mixture of kaolin and hydrous 

 silica. By treating the rock with caustic potash, Dr. Howe dissolved 

 over 7 per cent, of silica from it. The solution used contained 50 per 

 cent, of caustic potash (K O H.); in the first experiment 8.71 per cent, 

 of silica was dissolved, and in the second 7.93 per cent, of silica. This 

 determination is an indication that the hardening of the rock on expos- 

 ure is due to the presence of this hydrous silica, which might be, in 

 ])art at least, in a gelatinous condition in the rock, when soaked with its 

 quarry water. Owing to the nature of the components it is not easy 

 to calculate the mineral nature of the phosphate, which is a])parently 

 different in the two specimens analyzed. In the first case the acid is 

 apparently combined with alumina and in the second case with lime. 



National Museum, June 29, 1881. 



