40 PBOGEESS . ITS LAW AND CAUSE. 



probably depends upon that multiplication of effects which 

 we have seen to be the cause of progress in general, so fur 

 as we have yet traced it. 



When, leaving the development of single plants and 

 animals, we pass to that of the Earth s flora and fauna, the 

 course of our argument again becomes clear and simple. 

 Though, as was admitted in the first part of this article, 

 the fragmentary facts Palaeontology lias accumulated, do 

 not clearly warrant us in saying that, in the lapse of geo 

 logic time, there have been evolved more heterogeneous 

 organisms, and more heterogeneous assemblages of organ 

 isms, yet we shall now see that there must ever have been 

 a tendency towards these results. We shall find that the 

 production of many effects by one cause, which, as already 

 shown, has been all along increasing the physical hetero 

 geneity of the Earth, has further involved an increasing 

 heterogeneity in its flora and fauna, individually and col 

 lectively. An illustration will make this clear. 



Suppose that by a series of upheavals, occurring, as 

 they are now known to do, at long intervals, the East In 

 dian Archipelago were to be, step by step, raised into a 

 continent, and a chain of mountains formed along the axis 

 of elevation. By the first of these upheavals, the plants 

 and animals inhabiting Borneo, Sumatra, New Guinea, and 

 the rest, would be subjected to slightly modified sets of 

 conditions. The climate in general would be altered in 

 temperature, in humidity, and in its periodical variations ; 

 while the local differences would be multiplied. These 

 modifications would affect, perhaps inappreciably, the entire 

 flora and fauna of the region. The change of level would 

 produce additional modifications : varying in different spe 

 cies, and also in different members of the same speciee, 

 according to their distance from the axis of elevation. 

 Plants, growing only on the sea-shore in special localities, 

 might become extinct. Others, living only in swamps of a 



