December 31, 1900] 



SCIENCE 



945 



prevalent, it seemed beyond belief that 

 great sheets of ice could have crept over 

 large portions of the habitable parts of 

 Europe and North America some thou- 

 sands or tens of thousands of years ago. 

 Belief in this was made easier, however, 

 by the view also then prevalent that the' 

 earth had been greatly cooled in the prog- 

 ress of the ages, that the atmosphere had 

 been much depleted by the formation of 

 coal, of carbonates and of oxides, that the 

 ocean had been reduced by hydration and 

 entrance into the earth, and that thus a 

 stage had been reached that made possible 

 an epoch of depressed temperature and of 

 glaciation. The ice age, thus theoretically 

 associated, came to be widely regarded as 

 but the first stage in a series of secular 

 winters destined to lead on to the total 

 refrigeration of the earth. This view was 

 abetted by the theory of a cooling sun. 

 The depleting and the cooling processes 

 were regarded as inevitably progressive, 

 and the final doom of the earth as thus 

 foreshadowed in the near future, geolog- 

 ically speaking. 



But opinion was scarcely more than ad- 

 justed to this view when the geologists of 

 Australia, of India and of South Africa, 

 severally and independently, and later 

 those of South America presented evi- 

 dences of former glaciation over e.xten- 

 sive areas in those low latitudes. The 

 typical marks of glaciation were indeed 

 traced even up to and a little acro.ss the 

 tropical circles from the south, in Aus- 

 tralia, and from the north, in India. 

 Moreover, all the.se were reported from 

 strata of Permian or late Carboniferous 

 times, i. e., from the .sixth or .seventh of 

 the technical "periods." For a score of 

 years the body of geologists not in im- 

 mediate contact with the evidence itself, 

 doubted the interpretation, but the grow- 

 ing evidence grew at length to be utterly 

 irrefutable. There seems no rational es- 

 cape 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 read- 

 able 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 Black- 

 welder have described glacial deposits of 

 early Cambrian age in the valley of the 

 Yangtze in China in latitudes as low as 

 31°. Howchin and David have described 

 glacial formations of similar age in Aus- 

 tralia. 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. Pro- 

 fessor Coleman has offered what he deems 

 good evidence of glaciation much farther 

 back at the base of the Huronian in Can- 

 ada, but some skepticism as to its verity 

 has yet to be overcome. 



Even more pointedly than the epochs of 

 aridity, do these early epochs of glacia- 

 tion .seem incompatible with the view of a 

 hot earth universally wrapt in a vaporous 

 mantle in early times. They favor the 

 alternative view of merely temporary 

 localized intensifications of climate which 

 life was able repeatedly to survive. This 

 seems to warrant the belief that life may 

 survive similar inten.sifications again and 

 again in the future. 



At present polar and alpine glaciation 

 are contemporaneous with aridity. There 

 are reasons for thinking that the past 

 glaciations and aridities were in some sim- 

 ilar way correlated and that they coop- 

 erated to give vici.ssitude to the climates 

 of certain geologic epochs. The known 

 epochs of glaciation, however, are fewer 

 than those of aridity. 



