A. Champernowne—U. Devonian in Devonshire. 359 
the exception only that the air on one side was perfectly dry, allow- 
ing radiation from the snow to pass without interruption into stellar 
space, while on the other side the air was moist, and full of aqueous 
vapour, absorbing the heat radiated from the snow, the snow-line 
would in this case undoubtedly descend to a lower level on the dry 
than on the moist side. No doubt more snow would be evaporated 
off the dry than off the moist side, but melting would certainly take 
place at a greater elevation on the moist than on the dry side, and 
this is what would mainly determine the position of the snow-line. 
In like manner the dryness of the air will in a great measure 
account for the present accumulation of snow and ice on Greenland 
and on the Antarctic continent. I have shown on former occasions that 
those regions are completely covered with permanent snow and ice, 
not because the quantity of snow falling on them is great, but 
because the quantity melted is small. And the reason why the 
snow does not melt is not because the amount of heat received during 
the year is not equivalent to the work of melting the ice, but mainly 
because of the dryness of the air, the snow is prevented from rising 
to the melting point. 
There is little doubt but that the cold of the glacial epoch would 
produce an analogous effect on temperate regions to that experienced 
at present on Arctic and Antarctic regions. The cold, although it 
might to some extent diminish the snow-fall, would dry the air and 
prevent the temperature of the snow rising to the melting point. It 
would not prevent evaporation taking place over the ocean by the 
sun’s heat but the reverse, but it would prevent the melting of the 
snow on the land during the greater part of the year. 
In places like Fuego and South Georgia, where the snow-fall is 
considerable, perennial snow and ice are produced by diametrically 
opposite means, as I have elsewhere shown, viz. by the sun’s heat 
being cut off by clouds and dense fogs. In the first place the upper 
surface of the clouds act as reflectors throwing back the sun’s rays 
into stellar space, and in the second place, of the heat which the 
clouds and fogs absorb, more than one-half is not radiated downwards 
on the snow, but upwards into space. And the comparatively small 
portion of the heat which manages to reach the ground and be 
available in melting the snow is insufficient to clear off the winter’s 
* accumulation. 
VI.—Uprrr Devonian 1n DEvonsHIRE.’ 
By A. CHamprrnowne, M.A., F.G.S. 
AVING read Mr. Reid’s letter on the above subject in the 
GuotocicaL Magazine for June, referring to the Chudleigh 
district, I beg to offer you a few lines of my own, in hopes of 
clearing up some confusion that may exist on the subject. 
In the first place, I cannot admit what Mr. Reid appears to imply, 
viz. that there are two Cephalopodous horizons in this small quarry 
(of Lower Dunscombe), a Clymenia limestone and a Goniatites in- 
tumescens stage. On the contrary, there is a passage from the upper- 
1 Received too late for insertion in the July Number.—Epir. Grou. Mac. 
