VI INTRODUCTION. 



overlooked, unless they advance some startling proposi- 

 tion as to the origin or remote antiquity of our own 

 race. There can be no use, however, in blaming the 

 popular taste ; nor would it be reasonable to expect that 

 every one should follow a scientific path, if his inclina- 

 tions do not lead him that way. The love of Nature 

 is not confined to any one period, and its votaries must 

 not feel disappointed, should their peculiar studies not 

 be shared by all their contemporaries. 



Before entering into the details of our marine Mol- 

 lusca, I would make a few more remarks as to their 

 distribution and structure. This I was prevented from 

 doing in the introductory part of the former volume by 

 an anxiety not to impose too long an exordium on the 

 patience of my readers. 



The sea-bed may be said, in the technical language of 

 lawyers, to be " land covered with water." Its outline, 

 if it could be viewed through an aquatic telescope, would 

 be seen to be irregular, and nearly as much diversified 

 as the surface of the earth. Mountains, hills, rocks, 

 gorges, valleys, and plains would be successively exhi- 

 bited in the submarine panorama, having often the same 

 bold and abrupt contour that gives so picturesque an 

 aspect to land scenery. Oceanic and tidal currents 

 represent rivers, corresponding with them in volume and 

 rapidity, and equally scooping out channels of various 

 degrees of width and depth. But we have good reason 

 to believe that lifeless deserts, like the great Sahara, are 

 wanting below the broad watery girdle which encircles 

 the globe and covers at least three-fourths of its extent. 

 It is true that, in certain inlets or arms of the sea, rivers 

 flowing into them may have sufficient strength and 

 velocity to sweep the middle of the channel, and thus 

 prevent the deposit of mud or other sediment which 



