| Reéxamination of American Minerals. 207 
alone or mainly which determines the depth to which species may 
live. It exerts an influence, and species fitted for cold waters may 
be found in the deeper seas where such waters occur. But the 
limit of descent depends on other influences. 
~ Looking at this table in another way, We see, as recognized b 
Prof. Forbes, that species which occur at or near the surface in 
Northern Scotland, are generally met with only at greater depths 
in the Mediterranean ; that is, the minimum depth is less in the 
former case than the latter. Thus Corbula nucleus has for its 
minimum depth in the Mediterranean six fathoms, and in the 
Horthern regions three fathoms. Psammobia JSerroensis has ten 
fathoms for the former, and three for the latter. Other examples 
Will be found in the above table, sufficient to illustrate the prin- 
ciple although many exceptions exist. Thus species that have a 
tange of 100 fathoms beyond Scotland may have the same. in 
the Mediterranean, except that in many cases they do not reach 
a8 Near the surface, where the waters are warm. 
_ the Crustacea of the same seas illustrate this subject in a 
Similar way. But the observations upon them have been made 
with less thoroughness and we have therefore confined our dis- 
S. 
cussions to Mollusk 
Dc 
Ant. XXIV.—Reixamination of American Minerals: Part Ist. 
~Emerylite; Huphyllite ; Litchfield Mica ; Unionite; Kero-' 
lite } Bowenite ; Williamsite; Lancasterite ; Hydro-magne- 
Sile; Magnesite : by J. Lawrence Smirx, M.D., Professor of 
Chemistry in the University of Virginia, and Georce J. Brusn, 
B., Assistant to the Chemical Department. 
1. Emerylite identical with Margarite. 
ap emerylite Was originally found by one of us on the emery 
Asia Minor, and also on the same mineral coming from the 
Clan Are! ipelago, Siberia, and China; it was subsequently 
