EFFECTS OF OSCILLATORY MOTION. 139 



36. Effects oj oscillatory motion. Great masses of water, sub- 

 ject, like the sea, to undulatory motion, present another order ot 

 facts ; not only are suspended substances deposited there in hori- 

 zontal beds, as a more weighty fluid would do, but the slightest 

 agitation does not permit any material particle to be solidly fixed 

 on planes of the least inclination, but tends, on the contrary, to de- 

 stroy all inequalities of the bottom. It is impossible to ascertain 

 positively these effects at the bottom of the sea ; but the immense 

 number of soundings, taken in all parts of the ocean by navigators, 

 show that all moving bottoms have very slight inclination; that 

 slopes, at an angle of half a degree, are rare, and that all above this 

 are exceptions : hence it follows, that in great masses of water, 

 beds formed by successive deposits must be entirely horizontal. 

 This fact is most clearly exhibited in certain lakes, which have 

 been entirely or in part dried up, where alternations of beds, of 

 every kind, are seen to be perfectly horizontal ; lakes Superior and 

 Huron furnish examples of this kind. 



37. This disposition of various matters deposited from water, 

 bed by bed, at the bottom of rivers, lakes, marshes, is termed strati- 

 fication; the deposits themselves are said to be stratified. This 

 circumstance eminently distinguishes deposits formed by water, 

 from those produced by igneous fusion, which are most frequently 

 massive, or irregularly divided. 



38. Nature of deposits organic remains. Beds of alluvium 

 are lormed of rolled flints, gravel, and sand, as well as of various 

 kinds of mud, analogous to matter called clay or argil. They 

 are more or less consolidated, as much by their own* weight, 

 as by waters charged with carbonate of lime, or various matters 

 which may penetrate them. In lakes, we see calca'reous and ar- 

 gilla'ceous marls, which have the property of hardening in the air, 

 as has been observed in certain half-dried lakes in Scotland, in 

 modern building-stone found in Hungary, and in lakes Superior 

 and Huron. Similar formations doubtlessly occur in the sea, as 

 waters are sufficiently calci'ferous to consolidate the sands thrown 

 on its coasts ; and the nature of upheaved deposits, in many places, 

 leave no uncertainty in this respect. 



These deposits are frequently filled with remains of all the organized 

 creatures now living on the surface of the globe. In river alluvium we find 

 remains of fluviatile shells that still live in the same localities, or land shells, 

 such as various snails, brought thither by rivulets; there are branches and 

 trunks of trees, masses of plants, more or less changed, sometimes partly 

 bitumenized, bones of terrestrial or aquatic animals, rarely human bones, 

 but frequently the remains of art, such as fragments of brick and pottery, 

 &c. 



36. What is the position of strata formed under the influence of undula 

 tory motion of water? 



.'{?. What is meant by stratification ? 

 38. Of what do beds of alluvium consist ? 

 33 



