350 PROCEEDINGS OF SECTION D. 



organisms, owing to their inhibitory effects, still greater resisting 

 powers when exposed to radio-activity, and enabled such organisms 

 to live in an area of greater radio-activity than their primeval 

 ancestor. At the same time the habits and physical characteristics 

 of such types gave them the power to exist in the rougher shallow 

 waters. The necessary modifications to enable organisms which 

 could exist in the shallower waters to survive on the fringe of the 

 primitive shore was probably the most gradual step. In the 

 shallower waters the effects of radio active emanations were 

 probably for the first time acutely felt, owing to intermittent 

 exposure of portions of an organism to the atmosphere, as is- 

 natural in shallow waters, and also to the greater concentration 

 of the emanation in such waters : these emanations would lead to 

 hypersensibility (? hyperaemia) of the superficies of the organism, 

 and this would aid the organism in drawing its supply of oxygen 

 partly direct from the air. Once this modification of a function- 

 became a permanent characteristic of a type, the transition to an 

 amphibious existence would not be great. 



At the same time, as the creation of a fauna was proceeding,, 

 similar steps were occurring in the creation of a flora. 



With the establishment of life in part existent on dry land the 

 first great period of the earth's biological history may be regarded 

 as closed, although this is only arbitrary. It was the period of 

 excessive and destructive radio-activity. At the end of this period 

 the natural radio-activity had waned a little, and it was possible 

 for life to exist with weaker radio-active inhibitory screens, and 

 also greater screens were developed ; organisms also had become 

 modified, and developed greater resisting powers to radio-activity 

 by means of artificial coverings, e.g., a shell, of false coatings, e.g., 

 the viscous material covering a worm and of integuments. 



The secondary period was the imperceptible modification of 

 the primary period. It was the period of irritative radio-activity, 

 the effects of the latter being insufficient to destroy life to the same 

 extent as in the primary, and the effects of irritation therefore 

 became the predominant feature. This was due to the waning of 

 the natural radio-activity combined with the deposition on the 

 primeval barren lands of a radio active screen of dead organic 

 material, which was originally a wind-blown drift from the primi- 

 tive beach. The dry land would be naturally divided into radio- 

 active areas, varying in intensity from the thickness of this deposit 

 and the amount of radio-active substance present. At the same 

 time it must be remembered that geological changes were pro- 

 gressing throvigh all ages, and evolution of the elements was leading 

 to deposits varying in their composition, distribution and quantity. 

 As the inhibitory effect of the various elements on radio-activity 

 varies directly as their atomic weights, it is evident that the 

 geological changes had considerable influence in the delineation 

 of the radio-active areas and their intensity and form of activity. 

 Thus as life spread on the dry land it was exposed to all degrees 

 and types of activity ; it also came more acutely within the sphere 



