250 C. Lloyd Morgan — Physiography. 



energy. Animals depend on plants, directly or indirectly, both for 

 the food they eat and for the air they breathe. In the absence of 

 sunlight plants would be unable to decompose the vast quantity of 

 carbonic acid which animals breathe forth : and thus their source 

 of carbon and our source of oxygen would be cut off. 



Another question must now be put and shortly answered. The 

 sand and clay and chalk which form our cliff were laid down 

 beneath the sea ; how come they now to form dry land ? Now it is 

 clear that one of two things must have taken place : either the level 

 of the sea has been depressed or that the land has been raised. 

 Geologists do not hesitate to say that it is the land which has under- 

 gone the change in level, while the sea has remained stationary. 

 The sea is, in fact, more stable, more constant, more ancient than 

 our oldest continents. All land is, on the other hand, subject to 

 changes of level. In the Himalaya mountains shells, which once 

 lived in the sea, are found at an elevation of 16,000 feet above the 

 level of the ocean. The northern part of Scandinavia is even now 

 slowly rising, while the southern portion is undergoing depression. 

 But how ? There lies the question. 



It is now well known that the Earth is, in the interior, in an in- 

 tensely heated condition. In deep wells and mines the temperature 

 rises about 1° Fah. for every sixty feet we descend. The melted 

 lava poured forth during volcanic eruptions gives us some idea of the 

 temperature comparatively near the surface. The centre of the 

 Earth must then be hot beyond conception. But it is gradually 

 cooling. Heat is flowing outwards through the crust into space : the 

 cooling of the Earth is accompanied by contraction of the mass of the 

 Earth : and unequal contraction produces areas of depression and 

 elevation. 



Is this clear ? Perhaps a comparison of great things with small 

 will make it clearer. The human mind seems at times to fail to 

 grasp facts which are, in truth, simple, but which from their magni- 

 tude are hard of conception. If, for instance, we stand on a high 

 peak and look out over a portion of a great mountain chain, and see 

 the grand summits standing out along the central ridge, it is difficult 

 to conceive how this grand upheaval could have been produced ; and 

 perhaps the mind, wearied with the attempt to grapple with a subject 

 almost too great for its powers, finds relief in the thought, that the 

 mighty elevation was due to some great cataclysm or convulsion of 

 Nature, concerning the cause of which — as a matter beyond our ken 

 — it would be rash to speculate. And if it were then suggested that 

 mountain chains, such as that in the midst of which we were standing, 

 must be the inevitable result of the contraction of a cooling globe, it 

 may be that our understanding would reject a conclusion which it 

 could not at once grasp. 



But if when we have left the mountain top, we take up a withered 

 apple of last year's growth, the consideration of its surface may help 

 us to understand that which before was so hard to comprehend. 

 When we plucked that apple, a year ago, its surface was smooth, and 

 the skin was stretched tightly over the fruit beneath. But since that 



