GEOLOGICAL CLIMATE IN HIGH LATITUDES. 359 



summer and winter. They may occur several times in a summer, or 

 not at all, or once in several years, or where there is absolutely no 

 change of seasons. I have seen a hard and woody stem of Che?iopo- 

 dium album, not more than four months from the seed, in which were 

 eight well-formed rings. Dr. Gray says there is " a woody Phytolacca 

 which makes at least twice as many layers as it is years old," and 

 that cycads require several years for one layer. The orange and 

 lemon, in green-houses, where seasons can hardly be said to be known, 

 form ring's as well defined as those of our forest-trees. On the Ama- 

 zon, as may be seen in a collection of woods now in Yassar College, 

 the rings are very apparent in some species, while in others equally 

 exogenous none can be seen. The mangrove, which grows in the 

 tropics on the sea-shore between high and low water mark, where by 

 no possibility can there be any annual change either in temperature, 

 or from wet to dry, has the rings well developed.* These facts suffice 

 to prove that the existence of growth-rings is independent of the ex- 

 istence of seasons. 



I think it must be admitted that the teachings of geology are in 

 harmony with what would have been the climatic conditions in high 

 latitudes if the axis of the earth was then perpendicular (or nearly so) 

 to the ecliptic, provided that in some way the temperature could have 

 been kept up sufficiently. And, if there be anything in the influence of 

 environments, the lack of results corresponding to days and nights so 

 different as those, e. g., of Spitzbergen and Florida, is evidence that the 

 days and nights in those countries did not differ then as they now do. 

 If there was no such difference, the earth's axis then did not incline as 

 it does at the present day. 



The tilting of the earth, or, in other words, changing the direction 

 of its axis if gradual would occasion no perceptible disturbance. 

 Hence no conclusion is to be drawn from the absence of traces of such 

 a cataclysm as would have attended a change of the geographical posi- 

 tion of the poles. The latter, however slowly brought about, would 

 have necessitated a change in the position of the equatorial protuber- 

 ance, or, if the crust was too rigid for that, a change in the ocean suf- 

 ficient to overwhelm the land. The only possible effect of an increase 

 in the obliquity of the axis would be an increase in the length of the 

 days and nights in high latitudes followed by corresponding climatic 

 changes. These would have registered themselves in the plants and 

 animals of high latitudes, while near the equator the effect would be 

 scarcely perceptible. Days and nights in low latitudes would be only 

 slightly affected, consequently animal and vegetable life would con- 

 tinue as before. It is corroborative of such a tilting, that the plants 

 and animals in high latitudes, which, till near the end of the Tertiary, 



* See "American Journal of Science," 1878, Article XLV, "Is the Existence of 

 Growth-Rings in the Exogenous Plant Proof of Alternating Seasons ? " by the present 

 writer. 



