22 



THE NATURAL HISTORY OF 



rivers that flow into it ; and in the Caspian, where 

 the waters are of a nature very different from that 

 of the ocean. In many confined localities, as in the 

 lochs of Scotland, and the fiords of Norway, also in 

 many estuaries, the surface waters may be fresh, or 

 nearly so, whilst their depths are as salt as the open 

 ocean, so that in the same place we may have 

 creatures organized for very different states of sea- 

 composition living not merely in the immediate 

 neighbourhood of each other, but even, as it were, 

 superimposed. I was once greatly struck with this 

 fact, when dredging in the Killeries, along with 

 Robert Ball and William Thompson, an arm of the 

 sea in the wild and rocky district of Connemara, in 

 Ireland. The depth was some fifteen or twenty 

 fathoms, and the creatures inhabiting the sea-bottom 

 were characteristically marine. When taken out of 

 the water, they seemed to be unusually torpid, and 

 it was in vain we placed them in vessels filled with 

 the element of their native bay in order to tempt 

 them to display their variously-shaped delicate 

 organs. The cause of their languor soon became 

 evident, when we remarked a fisherman dipping a 

 cup into the water by the boat-side for the purpose 

 of procuring some to drink. The uppermost stra- 

 tum of the narrow and lake-like bay was purely 

 fresh, or nearly so, derived doubtless from the 

 numerous streamlets flowing into it, and from the 

 rain, over-sufficiently abundant in that mountainous 

 and picturesque district. The mollusca and radiata 



