46 ON CHANGES IN THE DISPOSITION 



ducirig an effect on the level of the water which flows 

 through it. Hence that of the sea becomes affected in 

 particular channels, and also differently affected in dif- 

 ferent places. Thus, in rising, it encroaches on the 

 land, while the land, from the causes just examined, is 

 also encroaching on the sea ; a double, and apparently 

 opposite effect, resulting from a common cause, while 

 leading to disputes which a little knowledge might have 

 prevented. Were there no currents or tides, and were 

 the, ocean in a state of absolute rest and equilibrium, 

 its level would unquestionably be every where raised by 

 the gradual addition of earth to its bottom and its shores. 

 But, compared to its great depth and extent, this can 

 produce no sensible effect ; and it is therefore to the de- 

 position of earth in tide-ways or currents, that the ele- 

 vations of the level of the sea are to be attributed ; ex- 

 cept, as must be obvious, in the case of an inclosed sea. 

 The truth of this reasoning is confirmed by observa- 

 tion : but encroachments of the sea may also follow 

 from the subsidence of the shores, or from their waste, 

 as must be obvious. In examining different examples 

 of these changes, we may, by attending to these consi- 

 derations, succeed in separating the different causes 

 whence they have originated ; and thus, often clear the 

 general question respecting the changes of the earth's 

 surface, from the obscurity in which it has been in- 

 volved by those who would admit only one cause, as 

 well as by those who have confused themselves through 

 ignorance or misapprehension. 



But if the chief observed variations in the level of 

 the sea consist in its depression, this expression pre- 

 judges the cause : the variation in question being that 

 of the relative position, at different periods, of the 

 common line which bounds the land and the water. 

 Such a change may arise from four causes ; namely, 



