4 GEOLOGY OF THE ISLE OF WIGHT 



very finest of all, under most favourable conditions, rarely 

 extending beyond 150, and never exceeding 300 miles 

 from land into the deep ocean. So gradually layer after 

 layer of sand and mud cover the sea bed round our coasts ; 

 and shells of cockles and periwinkles, of crabs and sea 

 urchins, and other sea creatures that have lived on the 

 bottom of the sea are buried in the growing layers of 

 sand and mud. As layer forms on layer, the lower layers 

 are pressed together, and become more and more solid. 

 And so we have got a good way towards seeing the making 

 of clay and sandstone with shells in them, such as we 

 saw in the sea cliffs and the quarries. 



But it is not only rain and rivers that are wearing the 

 land away. All round the coasts the sea is doing the 

 same work. We see the waves beating against the shores, 

 washing out the softer material, hollowing caves into the 

 cliffs, eating away by degrees even the hardest rock, leav- 

 ing for a while at times isolated rocks like the Needles to 

 mark the former extension of the land. Most people see 

 for themselves the work of the sea, but do not notice so 

 much what the rain and the frost, the streams and the 

 rivers are doing. But these are wearing away the ground 

 over the whole country, while the sea is only eating away 

 at the coast line. So the whole of the land is being worn 

 away, and the sand and mud carried out into the sea, and 

 deposited there, the material of new land beneath the 

 waters. 



How do these beds rise up again, so that we find them 

 with their sea shells in the quarry ? Well, we look at the 

 sea heaving up and down with the tides, and we think of 

 the land as firm and fixed. And yet the land also is con- 

 tinually heaving up and down very slowly, far too 

 slowly for it to be noticed, but none the less surely. The 

 exact causes of this are not yet well understood, because 

 we know but little about the inside of the earth. The 

 deepest mine goes a very little way. We know that parts 



