332 THE ZOOLOGIST. 



BIOLOGICAL SUGGESTIONS. 



EXTEBMINATION IN ANIMAL LIFE. 



Part I. — By Natural or non-Human Agency. 



By W. L. Distant. 



(Continued from p. 292.) 



To understand some processes of actual extinction of species, 

 it is necessary to study causes that tend toward that result, 

 factors which alone are not destructive, but which combined, or 

 recurrent, eventually act as do a persistent series of non-mortal 

 ailments on the human constitution, sapping its vitality, and 

 rendering it vulnerable to an attack not essentially destructive. 

 In nature we meet with many of these sporadic phenomena, 

 which we consider much rarer than they really are, and this 

 partially from our paucity of observations and records, and also 

 largely incidental to our usually spending our existence in one 

 area. On the island of Sakhalin, which at present is of some 

 political notoriety, the peat-formation of the tundras, according 

 to Prof, von Krasnow, reaches in many places a thickness of 

 fifty feet, and beneath it upright fossil larch- stems, which have 

 been buried in situ, can often be seen. The destruction of these 

 woods might be ascribed to a change of climate, but another 

 explanation may also be found. " The snow, owing to the cold 

 and gloomy summer, lies as late as July under the shelter of the 

 forest on badly drained clayey soil. The surface, constantly 

 damp, becomes covered with a growth of swamp vegetation, 

 which more and more prevents the access of the summer air 

 and the thawing of the soil. Thus the conditions become 

 more and more unfavourable to the growth of the forest, till 

 even the moisture-loving larch gives place to the bare tundra. 

 All the wide plains of Sakhalin have therefore been trans- 

 formed into tundras and half-frozen peat-bogs, and a true 

 polar landscape prevails wherever mountains or hills are ab- 



