12 . GEOLOGY OF THE ISLE OF WIGHT 



the Southern Downs along the South Coast from 

 Shanklin to Chale. In the Central Downs the chalk 

 rises nearly vertically, and turns over in the beginning 

 of an arch towards the South. Then comes a big gap, 

 and the chalk appears again in the Southern Downs 

 nearly horizontal, sloping gently to the south. The 

 chalk was once joined right across the central hollow, 

 where now we see the villages of Newchurch, Godshill, 

 and Arreton. All that enormous mass of rock that once 

 filled the space between the downs has been cut away by 

 running water. 



An arch of strata like this fl, such as the one we are 

 looking at, is called an anticline. When the arch is re- 

 versed, like this U, it is called a syncline. Looking north 

 from the Central Downs over the Solent we are looking 

 at a syncline. The chalk, which dips down at the Culvers 

 and along the line of the Central Downs, runs like a trough 

 under the Solent, and rises again, as we see it on the other 

 side, in the Portsdown Hills. 



We might suppose the top of an anticlinal arch would 

 be the highest part of the country ; that, even if rain 

 and running water have worn the country down, that 

 would still stand highest, and be worn down least. But 

 there are reasons why this need not be so. For one thing, 

 when the horizontal strata are curved over into an arch, 

 they naturally crack just at the top of the curve, so 



and into the cracks the rain gets, and so a stream is 

 started there, which cuts down and widens its channel, 

 and so eats the land away. Again, the rising land only 

 emerges gradually from the sea, and the sea may cut off 

 the top of the arch before it has risen out of its reach. 

 Moreover on the higher land the fall of rain and snow is 

 greater, and the frosts are more severe ; so that it is just 



