of some Sedimentary Rocks. 235 



surfaces glimmering and slightly unctuous; it is completely 

 earthy, opake even upon the edges, and very soft, yielding with 

 ease to the nail ; the powder is not at all gritty. 



The parophite loses water when exposed to heat and turns 

 gray; it is but imperfectly decomposed by hydrochloric acid. 

 The following analyses were made by fusion with carbonate of 

 soda, and the alkalies were determined by decomposing a second 

 portion M^th fluor-spar and sulphuric acid. Analyses I. and II. 

 are of schistose parophite. III. of the botryoidal variety, and IV. 

 of the earthy schist which passes into I. 



I. II. III. IV. 



Silica .... 48-60 48-42 49-13 48-10 



Alumina . . . 27-90 27-60 27-80 28-70 



Protoxide of iron . 5-67 4-50 5-90 4-80 



Lime .... 1-51 2-80 3-80 2-10 



Magnesia . . . 2-20 1-80 1-40 1-41 



Potash .... 5-30 5-02^ . «„, .rr 4-49 



Soda .... 1-91 2-78) 5-67bydiff. ^.53 



Water .... 7-40 6-88 6-30 8-40 



100-49 99-80 100-00 99-53 



Traces of manganese were found in all of them. 



These analyses show that the change consists only in a che- 

 mical union of the finely divided mixture which makes up the 

 sedimentary rock. Prof. C. U. Shepard described some time 

 since by the name of dysyntribite, an aluminous silicate which is 

 found in St. Lawrence County, New York, and had been mis- 

 taken for serpentine, which it resembles in colour, lustre, and 

 general appearance ; it has, according to him, a hardness of 3-5 

 to 4-0, and a density of 2"76 to 281. He gave the following 

 analytical results: — silica, 47-68; alumina, 41-50; protoxide of 

 iron, 5-48; water, 4-83; and traces of lime and magnesia; 

 = 99-49*. Notwithstanding the resemblance of this to the 



fiarophite of St. Nicolas, the differences in composition, partieu- 

 ariy in the large amount of alumina and the absence of alkalies, 

 according to the analyses of Prof. Shepard, were such that we 

 supposed the rocks to be distinct. 



The recent analyses of dysyntribite by J. Lawrence Smith and 

 G. Brush have, however, shown that this substance, although of 

 variable composition, contains a large amount of potash, and in 

 many specimens approaches the parophite. They obtained from 

 44-7 to 46-7 per cent, of silica, and from 4-7 to 6-3 of water; 

 while the alumina varied from 31 to 35 per cent., and the oxide 



* Report of the Americau Association for the Advaiiccment of Science, 

 vol. iv. ]). 311. 



R2 



