Trans. N. Y. Ac. Sci. 86 April 14, 
space just equalled what was brought in by ocean and aérial currents. 
Calling the heat from these sources A, and that from the sun B, the 
summer heat must have been A+ B. The difference between the 
seasons at the present day is enormous. It could not have been small 
at any time. Yet, somehow, ‘‘ through the whole hemisphere—and we 
may say the whole world—there was a genial atmosphere for one 
uniform type of vegetation, and there were genial waters for corals and 
brachiopods.” * 
The influence of light upon vegetation is one of the clews which 
may lead to important results in the study of these ancient problems. 
At the present time the mode of applying the actinic forces varies 
greatly in high and low latitudes. In Spitzbergen, for example. the 
sun shines uninterruptedly for four months, then the days begin to 
grow shorter, till finally a night sets in, lasting four months. In low 
latitudes, the supply of chemical rays is continuous for only about 
twelve hours, and then ceases for a night of not greatly different length. 
Light is as necessary to plant life as heat, and its evidence, as to 
whatever it is capable of. testifying about, is far more reliable ; for 
only the inclination of the earth’s axis can affect the length of the 
days, while the flow of the Gulf Stream and other ocean currents, the 
lay of the land, and the arrangement of the land and water, have a 
great effect upon temperature. 
The influence of environment on plants and animals has been shown 
by Mr. DARwIN and his followers to be very great. Unfavorable 
environments cause old species to disappear, and the new species, what- 
ever their cause, are in harmony with the environments amid which 
they have their birth. It seems, therefore, incredible that in 
Paleozoic and much later times, species, identically the same, could 
‘have flourished luxuriantly,” for example, in Spitzbergen and 
Florida, for millions and millions of years, unaffected by such great 
differences in the mode of supplying the chemical rays necessary for 
their very existence. The argument becomes stronger when we re- 
flect that during those years there were, from period to period, enor- 
mous changes in species—in some cases entire extermination t—new 
ones taking their place ; yet everywhere, from the tropics to the poles, 
in each period one type was found. Identical species were found in 
all latitudes. 
It seems, if possible, still more incredible that in later times, say in 
the Miocene, species should originate in Spitzbergen and Upper 
* Dana’s Manual Geol., p. 352. See also, in same work, all the earlier ‘‘ Climates.” 
+ See Dana’s Manual, ‘* Hxterminations.” I quote one statement, page 485: ‘* Not only 
every species, but also every Mesozoic genus, with perhaps one or two exceptions, became ex- 
tinct at or near the close of the era.” 
