THE STRUCTURE OF THE ISLAND n 



so on. But these layers of shale with shells in them, and 

 layers of limestone made of shells, must have been laid 

 down at first fairly flat on the sea floor; but as they 

 were upheaved out of the sea they have been tilted, so 

 that we now see them in an inclined position. And when 

 we come to the chalk, we should see, if we looked at the 

 end of the Culver Cliffs from a boat, that the lines of 

 black flints that run through the chalk are nearly vertical. 

 The strata there have been tilted up on end. 



In describing how strata lie, we call the inclination of 

 the strata from the horizontal the dip. The direction of 

 a horizontal line at right angles to that of the dip is called 

 the strike. If we compare the sloping strata to the roof 

 of a house, a line down the slope of the roof will mark the 

 direction of the dip, the ridge of the roof that of the strike. 

 The strata we are considering dip towards the North ; 

 the line of strike is East and West. 



Returning towards Sandown we see the strata dipping 

 less and less steeply, till near the Granite Fort the rocks 

 on the shore are horizontal. Continuing our walk past 

 Sandown to Shanklin we pass the same succession of rocks 

 we have been looking at, but in reverse order, and sloping 

 the other way. It is not very easy to see this at first, for 

 so much is covered by building ; but beyond Sandown we 

 see Sandstone Cliffs like the Red Cliff again, the strata 

 dipping gently now to the south, and in the downs above 

 Shanklin we see the chalk again. So we have the same 

 strata north and south of Sandown, forming a sort of 

 arch. But the centre of the arch is missing. It must 

 have been cut away. We saw that the land was all being 

 eaten away by rain and rivers. Now we see what they 

 have done here. Go up on to the Downs, and look over 

 the central part of the Island. We see two ranges of 

 downs running from east to west, the Central Downs of 

 the Island, a long line of chalk down 24 miles from the 

 Culver Cliff on the east to the Needles on the west ; and 



