88 BULLFTIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Thomas Russell (1895, p. 98-100) gives a few statistics regarding 
the falls of hail as follows: — Hail falls during thunderstorms in 
summer and during the hottest part of the day. It rarely forms 
layers six inches thick. On Aug. 13, 1851, hail fell in New Hampshire 
to the depth of 4 inches. On July 24, 1818, it fell on the Orkney. 
Islands to the depth of 16 inches, on August 17, 1830, in Mexico City, 
to the depth of 16 inches. In the Yellowstone valley in Montana a 
fall of 14 inches has been recorded... .Hail is more common at 15,000 
feet than at sea-level, it forms at elevations from 5,000 to 16,000 feet; 
the greatest size of hailstones is found below 5,000 feet. It falls most 
frequently on the lee side of rising ground... . There are on the average 
fifteen hail storms a year in France, five in Germany, and three in 
Russia. 
In the Antarctic region hail now falls but rarely. Commodore 
Wilkes alone reports two instances. Fog there gives rise to some 
crusts of ice. (Fricker, 1900, p. 244). 
Alfred R. Wallace (1892, p. 299) states that he had good authority 
for hail having once fallen on the upper Amazon at a place enly three 
degrees south of the equator and about 200 feet above the level of the 
sea. Humboldt (1852, 2, p. 217) instances a case of hail falling at 
Paruruma in the Orinoco valley on a plain near sea-level. He states 
that hail in the tropics generally falls only at an elevation of 300 
toises (about 600 meters). 
The Shaler Memorial Expedition encountered in July, 1908, at an 
altitude of 900 meters on the campos of Sao Paulo between Bury 
and Faxina (p. 13), a hailstorm which covered the ground as thickly 
with hail as do many similar storms in New York and New England. 
I cite these instances of hailstorms with their attendant circum- 
stances because hail presents us now with a means of precipitating ice 
at low altitudes in regions near the equator where snow never falls. 
Hailfalls appear to increase toward the hot regions of the globe and 
to diminish in frequency of occurrence towards the polar tracts. Thus 
the probability of glaciers originating from hailfalls in subtropical 
regions would seem to be as great as from snowfalls, provided the 
hailstorms came frequently enough to overcome the effect of melting 
due to the higher temperature of those parts of the earth’s surface. 
Hailstorms like thunderstorms are secondary movements of at- 
mospheric vapor normally engendered in the wake of cyclones of far 
greater size and with a much longer path, and we do not at present 
know what geographic conditions, if any, would cause in Permian 
times a succession of hailstorms sweeping with the regularity of 
