Cross and Hillebrand—Cryolite from Colorado. 271 
point the vapor, he says, evaporated from the sea and con- 
ensed on the land will be rain and not snow, but when the 
temperature of the water is near the freezing-point, snow ‘will 
be the result. A diminution, for example, in the heat brought 
by the Gulf Stream that would very greatly lower the surface 
temperature of the sea surrounding Great Britain would, he 
says, bring about a heavy snow-fall and lead to permanent 
snow and ice, Again he maintains ‘‘as there is no reason to 
suppose that the surface-temperature of the sea would be lower 
during winter in aphelion and high eccentricity, it follows 
that there will not be more snow than now in countries where 
rain is the rule, even in winter, all other things equal.” 
There is surely a fallacy lurking under this theory of M. 
Woeikof. Snow instead of rain is not, as he supposes, owing 
_ to the low temperature of the water from which the vapor is 
derived, but to the low temperature of the air where the vapor 
18 precipitated. Of course, when the surface of the sea is near 
the freezing-point, the air over the sea and the adjoining land 
is usually ass not far from the freezing-point, and conse- 
quently the precipitation is more likely to be snow than rain. 
If the air be cold as it generally is over a snow and ice 
covered country, a high temperature of the adjoining seas, 
Were this possible, would greatly increase the snow-fall because 
it would greatly augment the quantity of vapor which would 
- be available for snow. 
Edinburgh, Scotland, May Ist, 1883. 
Art. XXX.—Communications from the U. 8. Geological Survey, 
Rocky Mountain division. IV. On minerals of the Cryvlite 
group recently found in Colorado; by WHITMAN Cross and 
W. F. Hinvesran 
Iv this Journal, for October, 1882,* we announced, in con- 
nection with the description of zircon and other minerals from 
* Third series, vol. xxiv, p. 281. ; 
* P. Groth, “ Beitrage ne Kenntniss der natiirlichen Fluorverbindungen,” Zeit- 
schrift fiir Krystallographie, vii, pp. 375-388 and 457-493. 
