The Evolution of Climates. — Mansoii. 209 
The interpretation which the writer offers of these facts is 
simple. As the shrinkages of the crust took place, during the 
Tertiary and Quaternary, the weakest places in the land masses 
yielded, and the successive layers of lava composing the great 
lava plains were erupted and laid down at irregular locations 
and intervals. The final eruptions took place during the chill 
of the Ice age, and as the great loads of ice were laid down 
along the lines of maximum precipitation. 
That these eruptions commenced in Tertiary time is indis- 
putable; that they continued during subsequent time is mani- 
fested by finding side by side, and between successive layers of 
lava fossil forms akin to both Tertiary and modern types of 
life.* 
The heat, the energy, liberated in the vast inundations 
forming the Columbia lava plains yet remains in noticeable 
quantity; its manifestations in the geysers of Yellowstone park 
profoundly impress the investigator and illustrate one of the 
ways deep seated heat escapes from a forming crust. The pres- 
ent phenomena could all be compassed in a square mile and are 
insignificant in energy when compared with the manifestations 
which for ages must have characterized the greater portion of 
the entire area now covered by lava measured by thousands 
of feet in thickness. 
To no other cause can we attribute the checking of the 
great Laurentide glacier in its mighty invasion than to the 
warm air and rain which, continually passing over and falling 
upon the lava plains, made the Missouri a warm river during 
the Ice age, and made the unglaciated area the last resting 
place for Tertiary forms, and the undisturbed graveyard for 
their remams. 
*Bulletin No. 108, U. S. Geo!. Survey, Appendix, p. 104. 
