XX 



INTRODUCTION. 



contain many of the materials which were carried up from the 

 surface of the earth ; (45) and in cases of violent action, sheets 

 of water will be frozen into cakes of ice, which will break into all 

 sorts of shapes and angles on reaching the surface of the earth. 1 



1 Mr. Howard says, " On the 21st of June, 1817, the thermometer at Bath in 

 the shade stood at 86, and on the same day at Lyneham,a water spout inundated 

 a considerable quantity of land and occasioned a rapid rise of the Avon. At 



