| → level. 1859 1860 1861 1866 |
| level, as well as the subsequent subaerial degradation. 1869 1872 |
|
|
and great changes in the mineralogical composition of consecutive formations, generally implying great changes in the geography of the surrounding lands, whence the sediment
derived,
with the belief of vast intervals of time having elapsed between each formation. |
|
|
can, I think, see why the geological formations of each region are almost invariably intermittent; that is, have not followed each other in close sequence. Scarcely any fact struck me more when examining many hundred miles of the South American coasts, which have been upraised several hundred feet within the recent period, than the absence of any recent deposits sufficiently extensive to last for even a short geological period. Along the whole west coast, which is inhabited by a peculiar marine fauna, tertiary beds are so
developed, that no record of several
and peculiar marine faunas will probably be preserved to a distant age. A little reflection will explain
along the rising coast of the western side of South America, no extensive formations with recent or tertiary remains can anywhere be found, though the supply of sediment must for ages have been great, from the enormous degradation of the coast-rocks and from muddy streams entering the sea. The explanation, no doubt, is, that the littoral and sub-littoral deposits are continually worn away, as soon as they are brought up by the slow and gradual rising of the land within the grinding action of the coast-waves. |
|
| We may, I think,
conclude that sediment must be accumulated in extremely thick, solid, or extensive masses, in order to withstand the incessant action of the waves, when first upraised and during
oscillations of
→level. Such thick and extensive accumulations of sediment may be formed in two ways;
|
