6 4 



SYNCLINAL AND ANTICLINAL DIP. 



versed. Horizontal beds necessarily have no dip. Dip is a property 

 of an inclined plane which causes the plane of a stratum to intersect 

 the plane of the horizon. 



The angle of dip is locally often due to the solidity and resistance 

 to flexure of thick deposits. But the direction of dip of one deposit 

 usually governs that of the beds above and below. Changes in the 

 direction of dip are due to the ways in which the strata are folded. 

 In the mountains of Wales the dip constantly changes ; and therefore 

 dip enables us to discover the crumpling and folds of the earth's crust. 

 East of the Pennine chain the rocks all dip to the east ; and west of 

 that range there is in much of the country a corresponding dip to the 

 west. Dip, no matter how simple it may appear in a single section, 

 is always a part of a fold of the earth's crust. These folds are either 

 downward and trough-like, or upward and ridge-like, though the rocks 

 themselves often appear on the surface in forms which may suggest to 

 the eye neither one nor the other. Thus the chalk of the Chiltern 

 Hills dips to the south-east, and passing under the ground reappears 

 in the North Downs which dip to the north. Hence the chalk has 

 there a basin or trough-shaped fold, and this complex dip is termed 

 a synclinal dip. Whenever a stratum is inclined in two opposite 

 directions so that the dips converge or meet downward, it is synclinal. 

 Almost every coalfield exhibits synclinal dip, because a synclinal fold 

 by sinking the strata below the general level preserves them from 

 destruction. Mountains often have a synclinal structure. 



MOP] TTebog. 



Tig. 17. Synclinal Dip of the Bala Hocks in Moel Hebog, near Bedgellert, North Wales. 



Similarly, whenever a stratum is inclined in two opposite direc- 

 tions so that the dips converge upward, the inclination is termed 

 anticlinal. This is well seen in the mountain limestone of Derby- 

 shire, in the Mendips, and in the Wealden district of Kent, Surrey, 

 and Sussex. The anticlinal of Woolhope is a locality where the 

 succession of the Silurian rocks is shown. 



wsw 



ENE 



Fig. 18. Anticlinal Dip of the Silurian Rocks in the Valley of Woolhope. 



Thus it is manifest that where the dip is synclinal the newest 

 beds are in the centre of the fold, while where the dip is anticlinal 



