6 GEOLOGY OF THE ISLE OF WIGHT 



reasons, that the main mass of the earth is rigid as 

 steel. Still underneath the surface rocks there must 

 be a quantity of semi-fluid matter, like molten rock, and 

 on this the solid land sways about, as we see the ice on a 

 pond sway with the pressure of the skaters on it. So the 

 solid land, pressed by internal forces, rises and falls like 

 the elastic ice, sometimes sinking and letting the sea flow 

 over, then rising again, and bringing up the land from 

 beneath the sea. 



Again, as the heated interior of the earth gradually 

 cools by the radiation of the earth's heat into space, it 

 will tend to shrink away from the cooler rocks of the 

 crust. This then, sinking in upon the shrinking interior, 

 will be thrown into folds, like the skin on a shrivelled 

 apple. Seeing, as we often do, layers of rock thrown into 

 numerous folds, so as to occupy a horizontal space far less 

 than that in which they were originally laid down, we can 

 hardly resist the conclusion that shrinkage of the cooling 

 interior of the earth has been a chief cause of the greatest 

 movements of the surface, and of the lateral pressure we 

 so often find the strata to have undergone. 



As we study geology we shall find plenty to show that 

 the land does rise and fall, that where now is land the 

 sea has been, that land once stretched where now is sea, 

 though there is still much which is not well understood 

 about the causes of its movements. We have seen how 

 many of the rocks are made in the sea, the sandstones 

 and the clays, but there are two other kinds of rocks, 

 about which we must say a little. The first are the 

 Igneous rocks, which means rocks made by fire. These 

 rocks have solidified, most frequently in crystalline forms, 

 from a molten mass. Lava, which flows hot and fluid, 

 from a volcano, and cooling becomes a sheet of solid rock, 

 is an igneous rock. Some igneous rocks solidify under 

 ground under great pressure, and become crystalline 

 rocks such as granite. We shall not find these rocks in 



