264 THOUGHTS IN A GRAYEL-PIT. [xi. 



Heath, and the clays of Dogmersfield, and reappears 

 from underneath them again at Reading. 



Thus you at Odiham stand on the edge of a chalk 

 basin ; of what was once a sea, or estuary, with shores 

 of chalk, which begins at the foot of the High Clere 

 Hills, and runs eastward, widening as it goes, past 

 London, into the Eastern Sea. Everywhere under this 

 great basin is the floor of chalk, covered with clays and 

 sands, which, for certain reasons, are called by geologists 

 Tertiary strata. 



But what has this to do with a gravel-pit ? 



This first. That all the flints in this pit have come 

 out of the chalk. They are coloured, most of them, 

 with iron, which has turned them brown ; but they are 

 exactly the same flints as those gray ones in the 

 chalk-pit on the other side of the town. 



How do I know that ? 



I think our own eyes will prove it : they are the 

 same shapes, and of the same substance ; but as a still 

 surer proof, we find exactly the same fossils in them ; 

 sponges, choanites (which were something like our 

 modern sea- anemones), corals, and "shepherds 7 crowns" 

 as the boys call the fossil sea-urchins. The species of 

 all these, and of other fossils, in the chalk-pit and in 

 the gravel-pit, are absolutely identical. The natural 

 conclusion is, then, that the gravel has been formed 

 from the washings of the chalk. The white lime of 

 the chalk has been carried away in water by some 

 flood or floods ; the heavier flints have been left 

 behind. 



Stop now one moment, and think. You all know 

 how very few flints there are in the chalk-pit, in pro- 

 portion to the mass of chalk. You all know what vast 



