412 



THE NATURE BOOK 



The diagram on page 410 shows a 

 generahsed section through strata which 

 have been folded and then carved into 

 mountain and valley by destructive 

 forces. 



The broken lines indicate the form of 

 the country as it would exist if folding 

 alone had taken place, and the continuous 

 lines represent the outhne after the carv- 

 ing agents have been at work. 



It will be noted that in the synclinal 

 hill the beds dip or incHne into the in- 

 terior, and away from the sides, whereas 

 in an anticlinal hill the strata would 

 curve upwards in the interior, and would 

 run parallel with the flanks. 



Ruskin, in " Modern Painters," discusses 

 this question very fully, and shows that 

 when the different layers of rock dip 

 towards the middle we get the conditions 

 of maximum strength, whereas when the 

 slope is towards the exterior the slopes 

 are perilous and unstable. 



It is essential to the existence of the 

 older mountains that they should have 

 been able to withstand denudation, hence 

 Snowdon and the great majority of our 

 highest mountains are synclinal in 



structure. They are not valleys which 

 have been exalted, but the mountains 

 which, at one time, towered above them 

 have been made low. In a former article 

 we have seen that there is abundant 

 evidence to show that changes of level 

 have taken place at various points round 

 our shores. In fact, depression is now 

 going on in the neighbourhood of most 

 of our river estuaries. In view of this 

 let us consider the case of a river valley, 

 widening towards the sea, and gradually 

 sinking beneath the waters. The former 

 channel gives place to a broad inlet of 

 the sea, and if sinking continues until the 

 mouths of tributary streams are affected 

 we have V-shaped lateral bays running 

 up into the land from the main inlet. 



Thus we must attribute estuaries round 

 our coasts to the work of rivers rather 

 than the erosive power of the sea. 



What the sea has done has been to 

 drown pre-existing valleys. The principal 

 ports round our coasts, such as Liverpool, 

 Bristol, Southampton, London, and Hull, 

 all owe their importance to the existence 

 of " drowned valleys " such as we have 

 just described. 



J. LOMAS. 



HOW TO KNOW THE TREES 

 GROWING IN BRITAIN 



With Notes, descriptive and photographic, for their Identification 

 in all Seasons of the Year 



By HENRY IRVING 



THE WILLOWS— II 



THE GOAT WILLOW, OR SALLOvV 



THIS, with its aUies, the Grey Willow 

 and the Eared Willow, shows con- 

 siderable variation, from those just 

 described, in twigs, buds, and knaves and 

 in the time of flowering. Though the 

 Sallow may grow into a small tree, it is 

 generally met with as a considerable 

 bush, or as forming part of the hedgerow. 



The twigs are shorter and stouter, 

 the buds are more rounded and larger 

 than in the case of other Willows. The 

 catkin buds are especially large and 

 prominent. The leaf-scars are broader. 

 The leaves, generally, are oblong, but 

 sometimes they are rounded. Their upper 

 surface is wrinkled, of a more or less deep 

 green, their lower surface is bluish green. 



