Trans. N. V. Ac. Sci. 86 April 14, 



space just equalled what was brought in by ocean and aerial currents. 

 Calling the heat from these sources A, and that from the sun B, the 

 summer heat must have been A 4- 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 

 Palaeozoic 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 f — 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." 

 t See Dana's Manual, '■'' Exterminations.'''' I q\iote 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." 



