18 THE AGE OF THE EARTH 



deposited, of conditions not very dissimilar from those 

 which obtain to-day. Thus the attachments of marine 

 organisms, which are permanently rooted to the bottom 

 or on the shores, did not differ in strength from those 

 which we now find — an indication that the strains due to 

 the movements of the sea did not greatly differ in the 

 past. 



We have evidence of a somewhat similar kind to prove 

 uniformity in the movements of the air. The expanse 

 of the wings of flying organisms certainly does not differ 

 in a direction which indicates any greater violence in the 

 atmospheric conditions. Before the birds had become 

 dominant among the larger flying organisms, their place 

 was taken by the flying reptiles, the pterodactyls, and 

 before the appearance of these we know that, in Palaeozoic 

 times, the insects were of immense size, a dragon-fly from 

 the Carboniferous rocks of France being upwards of 

 two feet in the expanse of its wings. As one group after 

 another of widely dissimilar organisms gained control of 

 the air, each was in turn enabled to increase to the size 

 which was best suited to such an environment, but we 

 find that the limits which obtain to-day were not widely 

 different in the past. And this is evidence for the 

 uniformity in the strains due to wind and storm no less 

 than to those due to gravity. Furthermore, the con- 

 dition of the earth's surface at present shows us how 

 extremely sensitive the flying organism is to an increase 

 in the former of these strains, when it occurs in proximity 

 to the sea. Thus it is well known that an unusually 

 large proportion of the Madeiran beetles are wingless, 

 while those which require the power of flight possess it 

 in a stronger degree than on continental areas. This 

 evolution in two directions is readily explained by the 

 destruction by drowning of the winged individuals of the 

 species which can manage to live without the power of 

 flight, and of the less strongly winged individuals of 

 those which need it. In the far more stormy, treeless 

 Kerguelen Land, the whole of the known insect fauna, 

 except two Diptera and probably a moth, is wingless. 



The size and strength of the trunks of fossil trees afford, 



