J. Schiel on Phosphoric Acid in Igneous Rocks. 353 
° 
B 
pe 
= 
e contrary, we merely find extinctions which can 
no more furnish a basis for distinguishing two periods than could 
the destruction of the Bos primigenius or that of the Dodo. 
of the extinction of each species. Some investigations of this 
tion of bones to the Quaternary epoch without other details. It 
is important always where it is possible to determine accurately 
the position and the geological relations of the stratum which 
encloses them, and sometimes even to indicate whether they are 
found in the upper or the lower part of the stratum. It is impor- 
tant to examine with great care the bones in the deposits of the 
glacial epoch, for it is very probable that many species have 
extended even to that period. By such studies well directed we 
may obtain more accurate knowledge of this series of extinctions, 
and I doubt not we shall be more and more convinced that they 
have been gradual and successive. 
Art. XXXII—On the Presence of Phosphoric Acid in Igneous 
Rocks ; by JAMES SCHIEL. 
tar 
taric acid and some sulphate of magnesia added, and then the 
phosphoric acid precipitated with an excess of ammonia; the 
* Fownes (Prize Essay, 1845) demonstrated the general presence of phosphoric 
acid in erystalline recks,—Ebs. 
er ee 
