SOUTH-WEST IRELAND. 205 



away. On an open seaboard the sea can do little 

 work, unless it is assisted by wind, but in narrow 

 places the rush in and out must accomplish more or 

 less work every tide. 



It seems remarkable that the gravels of the Weald, 

 if fluviatile, should all be below the 350 contour-line, 

 like the gravels of the " Esker-sea " period in Ireland, 

 and the sea-gravels in North America. 1 



The gravels of the Weald are said to be fluviatile ; 

 no positive proof for this suggestion has, however, 

 been given ; and we have shown that many so-called 

 river-flats and river gravels are probably the ancient 

 bottoms of estuaries and the gravels of estuaries ; 

 as in an estuary sloping terraces of gravel become 

 formed, while terrestrial and fresh-water fossils may 

 not be uncommon; for estuary deposits are more likely 

 than river accumulations to have the bones of land 

 animals in them, as may be studied in any river during 

 floods, because all animals drowned are swept down 

 by the current, and their bodies deposited in the still 

 water of a lake or an estuary. If there are rivers 

 flowing into an estuary while the waters of the estuary 

 are denuding rocks, the gravels found in the estuary 

 will be composed of fragments of higher beds brought 

 down by the rivers ; while the local fragments will be 

 brought elsewhere according to the set of the tidal 

 and other currents ; and such gravels could not be 



3 Principal Dawson. 



