= XI PHENOMENA OF ORGANIC NATURE 335 
* finer particles of this detritus, or mud as we call 
it, sinks to the bottom. 
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Or, again, if you take a river, rushing down 
from its mountain sources, brawling over the 
_ stones and rocks that intersect its path, loosening, 
removing, and carrying with it in its downward 
course the pebbles and lighter matters from its 
_ banks, it crushes and pounds down the rocks and 
earths in precisely the same way as the wearing 
action of the sea waves. The matters forming the 
deposit are torn from the mountain-side and 
whirled impetuously into the valley, more slowly 
over the plain, thence into the estuary, and from 
the estuary they are swept into the sea. The 
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coarser and heavier fragments are obviously 
deposited first, that is, as soon as the current 
begins to lose its force by becoming amalgamated 
_ with the stiller depths of the ocean, but the finer 
_and lighter particles are carried further on, and 
ee held 
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| _ eventually deposited in a deeper and stiller portion 
of the ocean, 
It clearly follows from this that mud gives us a 
chronology; for it is evident that supposing this, 
which I now sketch, to be the sea bottom, and 
| _ Supposing this to be a coast-line ; from the wash- 
ing action of the sea upon the sicke wearing and 
_ grinding it down into a sediment of mud, hie. mud. 
_ will be carried down, and, at length, deposited in 
_ the deeper parts of this sea bottom, where it will 
form a layer; and then, while that first layer is 
