SCIENTIFIC SUMMARY. 
317 
sea- water, it ought also to occur in the hard parts of marine organisms 
•consisting of those salts ; and M. Dieulafait has always found it in them 
with a weight of not more than 1 centigramme. A further investigation 
showed that this rule applied also to the fossil remains of organisms, for 
120 species of Brachiopoda, from the whole series of formations from the 
•Silurian upwards, all furnished the spectrum of strontian with quantities 
of substance less than 1 centigramme. In the author’s opinion all deposits 
of gypsum, of whatever geological age, have been produced simply by the 
evaporation of sea-water at the ordinary temperature of each epoch ; and if 
this view be correct, and the seas of all times had the same constitution 
all specimens of gypsum ought to contain strontian. This was found to be 
the case in 188 samples of Triassic gypsum, 85 of Tertiary gypsum, 4 of 
gypsum with mica (so-called metamorphic gypsum), and 6 specimens of the 
ophitic deposits of the Pyrenees, and the strontian was found to be pretty 
uniformly diffused throughout the mass of each deposit. In mineral waters 
•also, as might be expected, strontian is at least very generally present in 
variable quantities. 
MINERALOGY. 
Heubachite. — Sandberger has given this name to a mixture of the hydrated 
•oxides of cobalt and nickel (with a little iron and manganese o^ide) which 
occurs in black flakes and occasional spherular forms, on the heavy spar of 
the St. Anton mine, in the Heubach Valley, near Wittichen. It has the 
hardness 2*5, a density of 3*44, and contains 65-5 per cent, of cobalt oxide 
and 14*5 per cent, of nickel oxide. — Neues Jahrbuch fur Mineralogie , 1877, 
.299. 
Sellaite. — Six years ago Striiver discovered a colourless transparent mineral 
associated with anhydrite at Geibroula, in Piedmont. Small fragments of 
this mineral were found to melt in the flame of a candle, and to be insoluble 
in water and in all acids with the exception of sulphuric acid, which caused 
the evolution of hydrofluoric acid. The acid solution contained 39*64 per 
•cent, of magnesia, and the chemical and physical characters of the mineral 
led Striiver to regard it as a magnesium fluoride analogous in composition to 
fluorspar. It received at the time the name given above. Cossa, of 
Turin, has recently noticed that the white amorphous powder having the 
•composition Mg Fl 2 separates, after fusion with potassium or sodium chloride, 
in brilliant crystalline plates. The pare fluoride fuses at the temperature at 
which cast iron melts, and forms on cooling large crystals having the specific 
.gravity of 2*856, and possessing identically the same form as Striiver’s 
mineral, which he found to be quadratic. Both the mineral and the artificial 
product are phosphorescent, exhibiting a violet light. 
The Origin of Mineral Oils. — At a recent meeting of the Russian Chemical 
Society, Mendelejeff presented a report on his examination of the deposits of 
mineral oil in the Caucasus and in Pennsylvania, and propounded a new and 
interesting theory as to its probable origin. He questioned the accuracy of the 
view generally held, of the oil being a product of the decomposition of the fossil 
remains of organisms. The occurrence of the oil near the earth’s surface is 
