Ch IIt -j SUBAQUEOUS DEPOSITS. 



them having thinned out and given place to others, or some- 

 times one of the masses, first examined, is observed to increase 

 in thickness to the exclusion of other beds. Besides this 

 limited continuity of particular strata, it is obvious that the 

 whole assemblage must terminate somewhere ; as, for example, 

 where they reach the boundary of the original lake-basin, and 

 where they will come in contact with the rocks which form the 

 boundary of, and, at the same time, pass under all the recent 

 accumulations. 



In almost every estuary we may see, at low water, analogous 

 phenomena where the current has cut away part of some newly- 

 formed bank, consisting of a series of horizontal strata of peat, 

 sand, clay, and, sometimes, interposed beds of shells. Each of 

 these may often be traced over a considerable area, some ex- 

 tending farther than others, but all of necessity confined within 

 the basin of the estuary. Similar remarks are applicable, on a 

 much more extended scale, to the recent delta of a great river, 

 like the Ganges, after the periodical inundations have subsided, 

 and when sections are exposed of the river-banks and the cliffs 

 of numerous islands, in which horizontal beds of clay and sand 

 may be traced over an area many hundred miles in length, and 

 more than a hundred in breadth. 



Subaqueous deposits. The greater part of our continents are 

 evidently composed of subaqueous deposits ; and in the manner 

 of their arrangement we discover many characters precisely simi- 

 lar to those above described ; but the different groups of strata 

 are, for the most part, on a greater scale, both in regard to depth 

 and area, than any observable in the new formations of lakes, 

 deltas, or estuaries. We find, for example, beds of limestone 

 several hundred feet in thickness, containing imbedded corals and 

 shells, stretching from one country to another, yet always giving 

 place, at length, to a distinct set of strata, which either rise up 

 from under it like the rocks before alluded to as forming the 

 borders of a lake, or cover and conceal it. In other places, 

 we find beds of pebbles, and sand, or of clay of great thick- 

 ness. The different formations composed of these materials 



