946 



SCIENCE 



[N. S. Vol. XXX. No. 783 



On the other hand, at several stages, as 

 already noted, abundant life, bearing all 

 the evidences of a warm-temperate or sub- 

 tropical character, flourished in high lati- 

 tudes. In Greenland, Spitzbergen and 

 other Arctic islands, are found the relies 

 of life not known to be able to live except 

 under conditions of genial warmth. These 

 imply former sub-tropical 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 be- 

 tween one another, we seem now forced to 

 the conception of profound climatic alter- 

 nations extending over the whole stretch 

 of known geologic time. Concurrent with 

 these alternations there may perhaps have 

 been variations in the constitution, as there 

 certainlj' were in the condition, of the at- 

 mosphere. 



If we turn to the relations of the waters 

 and the land, an analogous oscillating his- 

 tory presents itself. This was possibly 

 connected causally with the climatic oscil- 

 lations. At no time in the history recorded 

 by clear geologic testimony is there proof 

 of the absence of land, and certainly at 

 Ao 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 

 <'.omparable 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 exten- 

 sion of the sea. Wliile each gained tem- 

 porarily on the other, complete victory 



never rested with either. From near the 

 beginning of the readable record there ap- 

 pears to have been an unbroken continuity 

 of land life, and from a like eai'ly 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 as- 

 signed for the extension of the land are 

 those that deform the body of the earth, 

 deepening its basins and drawing off the 

 waters, 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 the land sur- 

 face 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 

 serioi^sly threatened, a regenerative move- 

 ment in the body of the earth intervened, 

 the land was again extended and the sea 

 again restricted. Here then, also, there 

 has been a reciprocal movement which, 

 while it has brought alternate expansions 

 of land life and of sea life, has, notwith- 

 standing, permitted the preservation of 

 both, and thus maintained the continuity 

 of the two great divisions of life. 



It appears, thiis, that in each of the 

 great groups of terresti'ial conditions upon 



