108 KECENT PEKIOD. [Ch. X. 



the use of Pleistocene in this work, for I find that the introduction 

 of such a fourth name (unless restricted solely to the older Post- 

 tertiary formations) must render the use of Pliocene, in its original 

 extended sense, impossible, and it is often almost indispensable to 

 have a single term to comprehend both divisions of the Pliocene 

 period.* 



RECENT PERIOD. 



It was stated in the sixth chapter, when I treated of denudation, 

 that the dry land, or that part of the earth's surface which is not 

 covered by the waters of lakes or seas, is generally wasting away by 

 the incessant action of rain and rivers, and in some cases by the 

 undermining and removing power of waves and tides on the sea 

 coast. But the rate of waste is very unequal, since the level and 

 gently sloping lands, where they are protected by a continuous cov- 

 ering of vegetation, escape nearly all wear and tear, so that they 

 may remain for ages in a stationary condition, while the removal of 

 matter is constantly widening and deepening the intervening ravines 

 and valleys. 



The materials, both fine and coarse, carried down annually by 

 rivers from the higher regions to the lower, and deposited in succes- 

 sive strata in the basins of seas and lakes, must be of enormous 

 volume. We are always liable to underrate their magnitude, because 

 the accumulation of strata is going on out of sight. 



There are, however, causes at work which, in the course of centu- 

 ries, tend to render visible these modern formations, whether of 

 marine or lacustrine origin. For a large portion of the earth's crust 

 is always undergoing a change of level, some areas rising and others 

 sinking at the rate of a few inches, or a few feet, perhaps sometimes 

 yards, in a century, so that spaces which were once subaqueous are 

 gradually converted into land, and others which were high and dry 

 become submerged. In consequence of such movements we find in 

 certain regions, as in Cashmere for example, where the mountains are 

 often shaken by earthquakes, deposits which were formed in lakes in 

 the historical period, but through which rivers have now cut deep 

 and wide channels. In lacustrine strata thus intersected, works of 

 art and freshwater shells are seen. In other districts on the borders 

 of the sea, usually at very moderate elevations above its level, raised 

 beaches occur, or marine littoral deposits, such as those in which, on 

 the borders of the Bay of Baise, near Naples, the well-known temple 

 of Serapis was embedded. In that case the date of the monuments 

 buried in the marine strata is ascertainable, but in many other in- 



* If geologists still think it convenient to retain the term Pleistocene, I would 

 recommend them to use it not in the sense originally proposed by me, nor in thf 

 somewhat vague manner in which it was applied by Edward Forbes, but in place 

 of Post-pliocene as this term is defined in the present work. 



