THE STORY OP THE EARTH 37 



something like a pear-shape during its plastic period, 

 and this would lead to the emergence of the land in the 

 northern hemispheres, and a predominant gathering of 

 the waters in the southern. With the later collapse of a 

 large part of the northern hemisphere, the balance 

 would be largely restored ; but the curious tendency of 

 the continents on the actual map of the world to run to 

 a point southwards might find some explanation on these 

 lines. That, however, is a precarious conjecture, and 

 the feature is still very obscure and variously interpreted. 



It would be unprofitable and somewhat monotonous to 

 follow our geologists I have chiefly consulted the latest 

 editions of Suess, Lapparent, Geikie, Le Conte, and 

 Chamberlin through the vast series of changes in the 

 earth's aspect which they reproduce for us. I will select 

 only the points which it will be most useful to bear in 

 mind when we come to deal with the evolution of living 

 things. 



For several million years the ocean and the rains wore 

 away the early masses of land, which continued to rise, 

 with occasional depressions, from the depths of the sea. 

 By the end of what is called the Silurian period large 

 continents were just underneath, or peeping out above 

 the level of the waters. Low-lying continents, with 

 broad and uncertain shores, relieved the monotony of 

 the ocean, and over all brooded the heavy atmosphere 

 that kept off the bright sunlight. The air was probably 

 poisonous, from its quantity of carbon a ; oxide, to animals 

 such as we now have ; nor does the evolution of animal 

 life seem yet to have reached the stage of land-life. 

 Some geologists imagine the swampy continents as 

 covered with large and primitive plant-growths, but the 

 evidence is, as we shall see, too scanty to justify us in 

 dwelling on that conjecture. The ocean ftself certainly 

 abounded in life of all kinds up to the level of the fish. 



