GOO ADDITIONAL CHEMICAL EXAMINATIONS. 



eluding, that the ocean, during that epoch, was both shallow and clear. It is also worthy of note that 

 the coral formations of the Devonian period, in the valley of the Ohio, Mississippi, and Red Cedar Rivers, 

 are found at localities where the streams form rapids, or low falls ; from which it appears probable, that 

 the Polyparia have erected their structures on submarine ridges of the Devonian seas, formed by the 

 principal anticlinal axes existing at that geological epoch. 



ARTICLE IV. 



ADDITIONAL CHEMICAL EXAMINATIONS BY D. D. OWEN. 

 ANALYSIS OF TWO MINERALS AND NOTICE OF A NEW EARTH. ?* 



While examining, in the summer of 1848, the north shore of Lake Superior, situated in Minnesota, 

 between Pigeon Point and Fond du Lac, particularly in the vicinity of Baptism River, I observed a 

 peculiar, soft, green mineral, diffused in the amygdaloidal traps. Though not in large masses, this mineral 

 was so abundantly disseminated in some of these rocks that the least blow of the hammer indented the 

 rock and left a whitish-green mark from the easily crushed particles of the soft green mineral in question. 



In the winter of the same year I undertook a chemical analysis of the mineral, and repeated it on 

 several varieties in the year following. 



The result showed it to be essentially a hydrated silicate of magnesia, and what appeared to be a new 

 earth, intermediate in its properties between magnesia and manganese. 



The colour of this mineral when pure is of a pale yellowish green ; consistence and hardness about that 

 of wax. Heated in a matrass it gives off water. Heated strongly alone in the forceps it whitens, but 

 does not exfoliate ; tinges the outer flame slightly green. In thin splinters it fuses on the edges. With 

 borax it dissolves with difficulty into a transparent bead, which has a greenish tinge when hot. With 

 soda it dissolves but very partially and very slowly. Heated with nitrate of cobalt, hardly any colour is 

 perceptible. Fused with four times its weight of carbonate of soda and potash in a platina vessel it gives 

 a white enamel, tinged on the edges only of a light blue. Some specimens of this mineral effervesce dis- 

 tinctly with acids ; but this is always from impurities. The pure varieties contain no carbonic acid. 

 Specific gravity, 2-548. It has not been found crystallized. 



Treated with hydrochloric acid, chlorine is evolved, and the greater part of the constituents, except 

 silica, dissolved. 



After the separation of the silica and the greater part of the magnesia, there invariably remained a whitish 

 mass, tinged slightly of a reddish-yellow or flesh-colour, which had a tendency to darken in the air : this 

 amounted to 18 or 19 per cent. When this was dissolved in just sufficient hydrochloric acid to take it 

 up, and afterwards boiled with excess of caustic potash, 4-6 per cent, of alumina separated, leaving about 

 13-5 of matter quite insoluble in that reagent; of this 1-5 per cent, was peroxide of iron, and about 12 

 per cent, the new earth above alluded to, contaminated with some magnesia, which had escaped solution 



in the excess of chloride of ammonium employed to remove it. 

 The composition of the mineral is therefore as follows : 



II— Water, .......... 18- 



Si— Silica, .......... 42- 



Mg — Magnesia, ......... 20-5 



New earth, with some Mg. not taken up by sal. amm. . . . . 10 to 12 



Al — Alumina, ......... 4 - 6 



Fe — Peroxide of iron, . . . . ..... . 1-5 



K— Potash, .......... 0-8 



Mn, .......... a mere trace. 



* Originally published in the Journ. A. N. S. 2d Ser. Vol. II. pt. 2, Jan., 1852. 



