54 MINERALOGY AND LITIIOLOGY, 



potash or soda, making a silicate, which is called soluble glass. This 

 substance is a valuable cement. Wood, when coated with it, is fire- 

 proof ; and eggs, after being dipped in it, will remain fresh. It is, be- 

 side, a great purifying agent, and nothing else put in the water will 

 give that j^ure whiteness to linen that can be obtained by the use 

 of this substance. There are many deposits in this state, which are too 

 small to be of commercial value, but which might be much more gener- 

 ally utilized by the people of the neighborhood. The substance has 

 been latterly employed as the basis of dynamite.* It is a bad conductor 

 of heat, and serves as a good jorotection for boilers and steam-pipes. 

 A detailed list of localities for this substance in this state is given in the 

 report above alluded to, by Dr. Edwards.f 



These deposits are still being accumulated. If the material at the 

 bottom of any stagnant pool of long standing is carefully examined with 

 the aid of the microscope, these minute plants will be found in immense 

 numbers. 



Dr. Jackson obtained seven and one half per cent, of phosphates of 

 lime and magnesia from a specimen from Hooksett.| Any such material 

 would make an excellent fertilizer for fields near at hand. I have myself 

 seen no such phosphatic infusorial earth, and attribute the presence of 

 such an amount as indicated by Dr. Jackson's analysis to some acci- 

 dental cause. 



39. IIypersthene [(Mg, Fe) Si O3]. 



This mineral is distinguished from other minerals related in compo- 

 sition to pyroxene by its orthorhombic crystallization. It occurs in the 

 gabbro of Watervillc. It is a constituent not often visible to the naked 

 eye, but is easily recognized by its optical properties observable in micro- 

 scopic sections, and by the circumstance that it possesses the same 

 peculiar interpositions that make it so noticeable elsewhere. 



The most remarkable occurrences of hypersthene in America are at 

 St. Paul's island, Labrador, and at one or two points in Canada. As 

 there observed, it has a deep brown color, and easy cleavage parallel to 

 the brachypinnacoid, and the microscopic sections show that, inlaid in 



*See Ann. Rep., G. H. Cook, State Geologist of N. J., 1874. 

 t Geology of New Hampshire. Hitchcock. Vol. I, p. 502. 

 % Geology of New Hampshire. Jackson, p. 185. 



