ON AQUEOUS AND IGNEOUS METEOltS. 731. 



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cumstaiices appear to indicate; the remains of animals inhaijiting hot countries, 

 and the marine productions of hot climates, which are frequently found in - 

 high northern latitudes, would induce us to suspect, that the position of the ' 

 earth's axis was at a former time very different from its present position { ' 

 and we can scarcely assign any other probable cause for this change, than ' 

 the casual interference, and perhaps incorporation, of a comet with the 

 earth. The probabilities of such an event, in the whole course of time, are 

 however so small, that we have no reason to be apprehensive of the chance 

 of its occurring in future, for it is not enough that a comet should approach • 

 so near to the earth as to be very powerfully attracted by it, its motion must 

 also be directed almost in a straight line towards the earth ; otherwise it might 

 only be inflected into a new orbit, and go off again, without having caused 

 any other disturbance than a partial overflow of the sea. 



The face of the globe has also been very materially changed in the course 

 of ages, by the gradual operation of the sea and of rivers. The sea has in- 

 croached in particular parts, and retired from others; and the mouths of 

 large rivers, running through low countries, have often been variously modi- 

 fied, by a deposition and transfer of the matter washed down from the land. 

 At Havre the sea undermines the steep coast, and recedes at Dunkirk, where 

 the shore is flat: in Holland the Zuyder Zee was probably formed in the 

 middle ages by continual irruptions of the sea, where only the small lake 

 Flevo had before existed; and the mouths of the Rhine have been consider- 

 ably altered, both in their dimensions and in their directions. The 

 mud, deposited by large rivers, generally causes a Delta, or triangular 

 piece of land, to grow out into the sea; thus the mouth of the Missis- 

 sippi is said to have advanced above 50 miles since the discovery of" 

 America; and the sea has retired from Rosetta above a mile in 40 years. 

 The mouths of the Arno and of the Rhone consist also in great measure of 

 new land. 



The meteors denominated shooting stars are observed to move in all direc- 

 tions, as well upwards as downwards, although they frequently seem to 

 have a tendency towards a particular quarter in the course of the same 

 evening. Their height is seldom less than 20 miles, and sometimes as 

 nmch as 100 or 200, but usually about 50; their velocity is commonly 

 about 20 miles in a second, wliich differs very little from that of the earth 



