488 RIVER DELTAS. 



or pulling down, there is also another process in con- 

 stant operation, namely that of building up of new 

 lands beneath the bed of the sea. As the general level 

 of the land becomes reduced, of course the bed of the 

 sea becomes proportionately raised by the process of 

 sedimentary deposit, the tendency being to create vast 

 marshy swamps along and in advance of the present 

 coast lines; many extensive areas of such lands already 

 exist in almost every part of the world; but it is near 

 the mouths of some of the great rivers that this 

 operation may be seen in active progress; in several 

 of these cases the sediment brought down by their 

 waters, for ages past, has accumulated, and formed 

 large, flat, low-lying " Deltas" at the point where they 

 enter the sea, so called from their resemblance in 

 shape to the Greek capital D or " delta," marked "A" 

 in that language. 



The deltas of the Nile, the Ganges, and the Amazon, 

 form leading instances in point, large territories of this 

 sort having formed at the mouths of each of these 

 rivers. So immensely extensive is the delta at the 

 embouchure of the Amazon, that considerable difference 

 of opinion has arisen among geographers as to whether 

 it ought to be regarded as such at all or not; if, how- 

 ever, this term is to be construed as meaning, a more 

 or less delta-shaped alluvial flat, deposited by the river 

 at the point of juncture of the fresh water with the 

 salt, then the vastness of its size cannot ' invalidate its 

 title to be considered a "delta." Its shape, however, 

 has in this instance been considerably modified by 

 tributary streams and changes in the channels of these 

 rivers; also it evidently includes some islands, which 

 existed at a former epoch off this coast, and which 



