Geology and Natural History. 81 
high specific gravity ; and further that, by the addition of dis- 
tilled water drop by drop, any required density, trom thee maxi- 
mum (Thoulet) 2°77, down to 1, may be obtained. If now the 
fine fragments of a rock be introduced into the solution, Slee. ice 
density is tem or less than that of the solution will float and all 
others will sink. By carrying on the process in a suitable vener 
and by yada, as circumstances require, the density of the m 
struum, the separation of several different minerals may be accom- 
lished. For the further discussion of the subj ect, as given b 
f. Thoulet, reference must be made to his valuable memoir on 
a Contributions a Pétude des propriétés physiques et Fag 
c. Min. 
France, ii, 17, 1881). This method has been exhaustively studicl 
by Golds chmidt, and the results given in his memoir w how 
much can be accomplished in this way that was aes ty 
any of the earlier methods of mechanical separation ; at the same 
time he calls attention to the conditions ss which success de- 
pends and to the various opportunities of error. The maximum 
density. obtained by him was 37196 but v veriog somewhat with the 
temperature. By the use of the solution Goldschmidt shows that 
with due care the specific gravity of a pure mineral in fragments 
can be obtained with an error of only 2 or 3 units in the fourth 
place of decimals. He determines in this way the specific gravity 
differ 
of a large series of specimens of ent kinds of feldspar and 
concludes that the method gives a sure means of separating the 
different species of the group when In regard to 
obtained by him in a number of 1 epital. ‘idee te haa’ also been 
—Mr. J. H. Cou 
describes, in the Transactions of the Royal Geological Society of 
Cornw wall, deer-horns, now in the British Museum, that were 
In some parts, gi : 
trved or reproduced in oxide of tin” and even contain in places 
» ata “Sei cm of this oxide. They are reported as havi en 
oe ‘aff rded bim on mm analysie 2°60 per hte of stannic ek 
ese 
introduced ingredients is small, ‘they were found, hes ineroseopie 
Am. Jour. Scr. Daim, Sanam, Vs XXII, No. 127.—Joxy, 
