The Evohitioti of Climates. — Mnnson. 169 
At the culmination of the Ice age the snow Hne was much 
lower than at present, and elevated lands* at all latitudes were 
glaciated particularly along lines of maximum precipitation ; 
the seas were intensely cold. It is evident that since the culmi- 
nation of the Ice age and in the establishment of the present 
climates there has been a rise in temperatures in the tropical, 
temperate and sub-frigid zones. 
There is also indisputable evidence that this rise in temper- 
ature is yet in progress. This accession of heat must therefore 
be accounted for by the correct application of laws and forces 
now acting, and to the writer it seems that it is not necessary to 
go outside of these known laws and forces to render a correct 
interpretation of the development of the zones of climate now 
existing. 
It will be observed that as the bottoms of the oceans were 
gradually brought to their point of maximum density and the 
lands deeply glaciated, the crust was shrunk in upon the in- 
terior mass by being uniformly chilled. The atmosphere 
was then cleared of clouds and heat rays from exterior sources 
permitted to reach the planetary surface. As previously noted, 
the moment a ray of solar heat reached the surface and melted 
a snowflake, that moment was the removal of the Ice age fore- 
shadowed, and the process of its removal outlined. 
That the isotherm marked by the glacier is yet slowly re- 
treating upward is recorded not only by tradition and history 
but geologically and physically, as observed by every scientist 
who has studied existing glaciers. 
This retreat is a positive proof of either a decrease in precip- 
itation on the tributary areas, a rise in temperature, of both of 
these agencies acting conjointly. There is no evidence to show 
that a decrease in precipitation is synchronously taking place 
over the sub-frigid, temperate and tropical regions of both 
hemispheres, as there is of the retreat of glaciers; and there are 
positive and active causes in force which must have effected, 
and are yet effecting an increase in temperature. It is also of 
geological record that the surface temperature of the oceans 
has risen since the Ice age, in spite of the cooling efTect of the 
*Except hot or warm lava-covered areas, and the protected or "un- 
glaciated areas" to the eastward of such lava overflows. 
