Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments / by Sir Charles Lyell.

  • Lyell, Charles, Sir, 1797-1875.
Date:
1865
Catalogue details

Licence: Public Domain Mark

Credit: Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments / by Sir Charles Lyell. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

    130/822 (page 108)
    lie applied the term almost precisely in the sense in which. I shall use Post-pliocene in this volume, and not as short for Newer Plio- cene. .In order to prevent confusion, I think it best entirely to abstain from 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 covering 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, be- cause the accumulation of strata is going on out of sight. There are, however, causes at work which, in the course of cen- turies, 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 aud 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 Bairn, * 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 the somewhat vague manner in which it was applied by Edward Forbes, but in place of Post-pliocene as this term is de- fined in the present work.