RIPPLE-MARKS AND RAIN-DROPS 



diagram (Fig. 36) will help to make it clear how 

 the pushing and crushing of the earth's crust 

 into wave-like folds such as you may see when 

 a tablecloth or carpet is not spread flat, results 

 in bringing the deep-lying strata to the surface, 

 so that we can walk along a cutting or cliff and 

 come to deeper and older rocks as we walk along. 

 Here (Fig. 37) is a specimen which shows 



Fig. 37. — RiiDple-marks pieseiN ed in ancient Triassic strata. 



ripple-marks still preserved as we see them 

 nowadays on the shore at low tide. The marks 

 of raindrops are also often preserved on such 

 slabs of rock, which once were soft wet sand. 

 On such surfaces we often find footprints, the 

 footprints of birds and of reptiles. In some 

 cases we do not know the animal itself (Fig. 38), 



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