66 WALKS AND TALKS. 



short duration, and the deposits at the distance ot ten miles 

 from laud are no longer conspicuous. In the vicinity of coral 

 reefs and islands the attrition of the waves imparts a milky 

 complexion to the sea, especially during the prevalence of a 

 storm, and the calcareous particles are floated sometimes a 

 hundred miles and more. But it is apparent that, as a rule, 

 the sea floats too little sediment to build up a formation in any 

 other than a very gradual manner. We noticed, also, in our 

 walk under the sea, that the bottom sediments grew thin with 

 distance from the shore, and that those of continental origin 

 ceased entirely at about two miles in depth. When now we 

 remember that the stratified rocks are over a hundred thou- 

 sand feet in thickness, we perceive immediately that the 

 process of sedimentation has been an extremely long one. 



We have then to consider what changes may have taken 

 place in the conditions of the world during so long a period. 

 Probably the nature of the sediments has been changed from 

 time to time by these changes in the physical conditions of 

 the planet. We do not wish to anticipate conclusions to be 

 rested on facts which have not yet fallen under our observa- 

 tion ; but every body has noticed that the surface of the earth 

 is undergoing changes ; and these, in thousands of years, must 

 aggregate amounts which transform the aspects of the planet. 

 We have lived to see lakelets filled ; new channels formed for 

 great rivers ; ocean beaches consumed by the waves ; hundreds 

 of miles of continental coasts upraised or sunken as in Chili, 

 Scandinavia, and Greenland ; new islands bursting into view ; 

 whole provinces shattered by earthquakes. Suppose our ob- 

 servation extended back a million years, and the tenor of 

 events had been the same as in modern times ; is it not cer- 

 tain that changes must have aggregated to such an extent that, 

 waking at times to distinct consciousness of the greatly 

 changed conditions, we should from aeon to seon have felt ready 

 to declare a new chapter of the world's history had begun ? 

 I think so reasoning only from the physical data \\ltirh, so 

 far, have engaged our attention. But we shall hereafter make 

 the acquaintance of many other facts which will confirm this 



