148 APPENDIX. 



stance, exhibited by such bodies, is one of the 

 most striking objects this country presents, and is 

 certainly the most terrific. They not unfrequent- 

 ly acquire a rotatory movement, whereby their 

 circumference attains a velocity of several miles 

 per hour. A field, thus in motion, coming in con- 

 tact with another at rest, or more especially with a 

 contrary direction of movement, produces a dread- 

 ful shock. A body of more than ten thousand mil- 

 lions of tons in weight,* meeting with resistance, 

 when in motion, the consequences may possibly be 

 conceived ! 



" The weaker field is crushed with an awful 

 noise : sometimes the destruction is mutual. Pieces 

 of huge dimensions and weight are not unfrequent- 

 ly piled upon the top, to the height of twenty or 

 thirty feet, whilst doubtless a proportionate quan- 

 tity is depressed beneath. The view of those stu- 

 pendous effects in safety^ exhibits a picture sublime- 

 ly grand, but where there is danger of being over- 

 whelmed, terror and dismay must be the predomi- 



* A field of thirty nautical miles square surface, and thirteen 

 feet in thickness, would weigh somewhat more than is here 

 mentioned. Allowing it to displace the water in which it floats, 

 to the depth of eleven feet, the weight would appear to be 

 10,182,857,142, nearly in the proportion of a cubic foot of sea 

 water to 64 lbs. 



