310 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1914. 
On the land the story of the climatic changes is different, but in 
general the equability of the temperature simulates that of the oceanic 
areas. In other words, the lands also had long-enduring times of 
mild to warm climates. Into the problem of land climates, however, 
enter other factors that are absent in the oceanic regions, and these 
have great influence upon the climates of the continents. Most 
important of these is the periodic warm-water inundation of the 
lands by the oceans, causing insular climates that are milder and 
moister. With the vanishing of the floods somewhat cooler and cer- 
tainly drier climates are produced. The effect of these periodic floods 
must not be underestimated, for the North American Continent was 
variably submerged at least 17 times, and over an area of from 
154,000 to 4,000,00 square miles. (Schuchert, 1910.) 
When to these factors is added the effect upon the climate caused 
by the periodic rising of mountain chains, it is at once apparent that 
the lands must have had constantly varymg climates. In general 
the temperature fluctuations seem to have been slight, but geograph- 
ically: the climates varied between mild to warm pluvial and mild to 
cool arid. The arid factor has been of the greatest import to the 
organic world of the lands. Further, when to all of these causes is 
added the fact that during emergent periods the formerly isolated 
lands were connected by land bridges, permitting intermigration of 
the land floras and faunas, with the introduction of their parasites 
and parasitic diseases,’ we learn that while the climatic environment 
is of fundamental importance it is not the only cause for the more 
rapid evolution of terrestrial life. Unfortunately, the record of land 
life, and especially of the animal world, is the most imperfect of all 
paleontologic records until we come to Tertiary time. The known 
mammal history is a vast one and, although very difficult to imter- 
pret from the climatic standpoint, we have in the work of Depéret 
(1909), Osborn (1910), and Scott (1913) glimpses into the many tem- 
perature fluctuations, faunal isolations, and intercontinental radia- 
tions of Tertiary time. The history of the Tertiary is the last one 
of at least three previous and similar records (Mesozoic, later and 
earlier Paleozoic) of vastly longer eras, taking us back to a time when 
the lands were without visible life. 
In conclusion, it is seemingly clear that the variability in the storage 
of solar radiation by the earth’s atmospheric blanket and by oceanic 
waters, and the consequent climatic variations of the past and present 
are due in the main to topographic changes in the earth’s crust. 
These telluric changes alter the configuration of the continents and 
oceans, the air currents (moist or dry), the oceanic currents (warm, 
mild, or cool), and the volcanic ash content of the atmosphere. 
1 This subject is fully discussed by R. T. Eccles, M. D., in the following papers: “ Parasitism and natural 
selection,’’ ‘Importance of disease in plant and animal evolution,” ‘‘The scope of disease,”’ and ‘“ Disease 
and genetics.’? Medical Record for July 31, 1909; Mar. 16, 1912; Mar.8 and Aug. 2, 1913. 
