March io, 1910] 



NATURE 



53 



over extensive areas in those low latitudes. The typical 

 marks of glaciation were, indeed, traced even up to and a 

 little across the tropical circles from the south, in Australia, 

 and from the north, in India. Moreover, all these were 

 reported from strata of Permian or late Carboniferous 

 limes, i.e. from the sixth or seventh of the technical 

 ■'periods." For a score of years the body of geologists, 

 not in immediate contact with the evidence itself, doubted 

 the interpretation, but the growing evidence grew at length 

 to be utterly irrefutable. There seems no rational escape 

 from the conclusion that mantles of ice covered large areas 

 in the peninsula of India, in Australia, in the southern part 

 of Africa, and in South .America, close upon the borders of 

 the tropics, at a time roundly half-way back to the beginning 

 of the readable record of life. 



On the basis of similar evidence, Strahan and Reusch 

 have announced glacial beds in Norway at a horizon much 

 lower but not closely determinate. Willis and Blackwelder 

 have described glacial deposits of early Cambrian age in 

 the valley of the Yangtse, in China, in latitudes so low as 

 31°. Howchin and David have described glacial forma- 

 tions of similar age in Australia. In the last two cases 

 the glacial beds lie below the strata that bear the Cambrian 

 trilobites ; in other words, they lie at the very bottom of the 

 fossil-bearing sediments, fifteen periods back, or 75,000,000 

 years ago on our rough scale. Prof. Coleman has offered 

 what he deems good evidence of glaciation much farther 

 back at the base of the Huronian, in Canada, but some 

 scepticism as to its verity has yet to be overcome.^ 



Even more pointedly than the epochs of aridity do these 

 early epochs of glaciation seem incompatible with the view 

 of a hot earth universally wrapped in a vaporous mantle in 

 early times. They favour the alternative view of merely 

 temporary localised intensifications of climate which life 

 was able repeatedly to survive. This seems to warrant the 

 belief that life may survive similar intensifications again 

 and again in the future. 



At present polar and alpine glaciation are contem- 

 poraneous with aridity. There are reasons for thinking 

 that the past glaciations and aridities were in some 

 similar way correlated, and that they cooperated to give 

 vicissitude to the climates of certain geologic epochs. The 

 known epochs of glaciation, however, are fewer than those 

 of aridity. 



On the other hand, at several stages, as already noted, 

 abundant life, bearing all the evidences of a warm- 

 temperate or subtropical character, flourished in high lati- 

 tudes. In Greenland, Spitsbergen, and other Arctic islands, 

 are found the relics of life not known to be able to live 

 except under conditions of genial warmth. These imply 

 former subtropical conditions where now only frigidity 

 reigns. 



In the light of these contrasted climatic states of aridity 

 and glaciation on the one hand, and of uniformity and 

 geniality in high latitudes on the other, intervening between 

 one another, we seem now forced to the conception of pro- 

 found climatic alternations, extending over the whole stretch 

 of known geologic time. Concurrent with these alterna- 

 tions, there may, perhaps, have been variations in the 

 constitution, as there .certainly were in the condition, of the 

 atmosphere. 



If we turn to the relations of the waters and the land, an 

 analogous oscillating history presents itself. This was 

 possibly connected causally with the climatic oscillations. 

 hX no time in the history recorded by clear geologic testi- 

 mony is there proof of the absence of land, and certainly 

 at no time is there a hint of the absence of an ocean, 

 whatever theoretic views may be held of the earliest 

 unknown stages. 



The progress of inquiry seems to force the conviction 

 that the land area in the earliest' stages of good record was 

 quite comparable to that of the present time, both in its 

 extent and in its limitations. Following down the history, 

 the land area seems at certain times to have been larger 

 than now, while at other times it was smaller. There 

 appears to have been an unceasing contest between the 

 agencies that made for the extension of the land and the 

 agencies that made for the extension of the sea. While 

 each gained temporarily on the other, complete victory 



1 Later evidence has removed this from many minds, including that of the 

 speaker. 



NO. 2IC6, VOL. 8,^,] 



never rested with either. From near the beginning of the 

 readable record there appears to have been an unbroken 

 continuity of land life, and, from a like early stage, an 

 unbroken continuity of marine life. Probably the history 

 of both goes back unbroken into the undeciphered eras 

 which precede the readable record, and no one to-day can 

 safely affirm the precedence of either over the other, 

 either in time or in genesis, whatever his theoretic leanings 

 may be. 



Among the agencies that may be assigned for the exten- 

 sion of the land are those that deform the body of the 

 (•arth, deepening its basins and drawing off the water-;, 

 while other portions are protruded and give renewed relief 

 and extent to the land. Among the agencies that make for 

 the extension of the sea are the girdling of the waves about 

 the borders of the land, and the decay and wash of land 

 surface, which is thus brought low at length and covered 

 by the advancing waters. If the deformation of the earth- 

 body were held in abeyance for an indefinite time, the 

 lowering of the land, the filling of the basins, and the 

 spreading of the sea would submerge the entire land surface 

 and bring an end to all land life. Great progress in such 

 sea-transgressions appears to have been made again and 

 again, until perhaps half the land was submerged, but 

 before land life was entirely cut off, or even very seriously 

 threatened, a regenerative movement in the body of the 

 earth intervened, the land was again extended, and the sea 

 again restricted. Here then, also, there has been a re- 

 ciprocal movement, which, while it has brought alternate 

 expansions of land life and of sea life, has, notwithstanding, 

 permitted the preservation of both, and thus maintained the 

 continuity of the two great divisions of life. 



It appears, thus, that in each of the great groups of 

 terrestrial conditions upon which life is dependent, ther.' 

 has been, through the known ages, vast as ;they are, an 

 oscillatory movement which has brought profound changes 

 again and again, but has never permitted any of the 

 disasters threatened in these movements to go far enough 

 to compass the universal extinction of life. These reciprocal 

 movements appear to be dependent upon a balancing of the 

 action of agencies that is scarcely less than a law of 

 equilibrium. It is not too much to regard this as a. regula- 

 tive system. A clear insight into the agencies of this 

 regulative system is rather a task of the future than an 

 attainment of the present, and I can only offer tentative 

 hints of what may prove to be its main factors, and beg of 

 you to accept them with due reserve. 



The preservation of the land against the incessant en- 

 croachments of the waters seems probably due to a 

 periodic deformation of the earth-body dependent on internal 

 dynamics not yet well understood, at least not yet demon- 

 strated to general satisfaction. The body of the earth 

 feeds its atmosphere through volcanic and other means. 

 How far this is merely a return of what has been absorbed 

 earlier it is not prudent here to say, as opinion is not 

 harmonious on this, and the evidence is as yet uncertain. 

 Much depends on the constitution of the earth's interio'', 

 and that in turn hinges on its mode of origin. Perhaps it 

 will be agreed generally that feeding from the interior is 

 one of the sources of supply which offsets the depletion of 

 ihe atmosphere caused by its union with earth substance, in 

 short, that the earth-body gives out as well as takes in 

 atmospheric material. Important or unimportant as this 

 may be, it is not apparent that there is in it any automatic 

 balancing suited to control the delicate adjustments requisite 

 for continuity of life. The ocean acts as an important 

 regulator by alternately absorbing and giving out tha 

 atmospheric gases as required by the state of equilibrium 

 between the water and the air. This action is automatic, 

 but has its limitations and peculiarities, and does not seem 

 wholly adequate. If we are able to name such an adequate 

 automatic action at all at present, it probably lies in the 

 molecular activities of the terrestrial and solar atmospheres, 

 and in the relations of these to the gravitative powers of the 

 earth and the sun. 



If analysis of the molecular action of the outer atmo- 

 sphere be pushed to its logical conclusions, it leads to the 

 conception of supplementary atmospheres, in part orbital, 

 filling, in an attenuated way, the whole sphere of the earth's 

 gravitative control. A similar study of the sun's atmo- 

 sphere suggests a similar supplementary extension, and this 

 extended portion surrounds and embraces the earth's 



