THE APPEARANCE OF LIFE ON THE GLOBE 337 



The least improbable chances of success seem as 

 if they ought to be met with in the exploration 

 of the polar regions. Our present knowledge of the 

 history of the formation of continents and mountain 

 ranges authorizes us to think that it is in the Arctic 

 and Antarctic regions that the earth's crust first 

 became cooler, contracted, and wrinkled. It is 

 there that the first continental ridges must have 

 emerged at an early date from the surface of the 

 first seas. These desolate regions have exhibited 

 from the most remote periods of the life of the globe 

 a character of stability and rigidity of the most 

 remarkable kind, as contrasted with the mobility 

 and lesser resistance of the earth's crust in the 

 temperate and equatorial regions. It is, therefore, 

 in the vicinity of the Poles that the earliest sedi- 

 ments may perhaps have escaped metamorphism 

 by reason of their rapid incorporation into conti- 

 nents and the absence of a heavy superposition of 

 later deposits. 



There is, no doubt, room for hope in this direction 

 of important revelations as to the ancestors of the 

 Cambrian and pre-Cambrian animals, especially if 

 some heat-wave passing over the terrestrial atmo- 

 sphere, or some inter-glacial phase like those which 

 must several times have occurred during Quaternary 

 times, were to temporarily free the polar continents 

 from their coat of ice, and thus uplift for us a 

 corner of the veil which still covers the all-absorbing 

 problem of the apparition of life on the globe. 



