NERITIC DEPOSITS 66i 



some extent also the pelagic life will be destroyed by such glidings 

 and the distribution of the fauna will be altered. Such a case has 

 been noted in connection with the rock slide at Elm. Such dis- 

 turbance might result in the sudden destruction of the entire ben- 

 thonic fauna, young and old alike, all stages being found together. 

 Above the mass of material which caused this destruction may come 

 a stratum carrying only remains of planktonic organisms without 

 sedentary benthos, which would return only after a while. (Heim- 

 A7-I57-) 



The Permanently Submerged or Neritie Zone (Flachsee, Shallow 

 Water or Thalassal Zone). 



This zone extends from the low-water line of the shore zone, a 

 somewhat variable line, to the edge of the continental shelf. Sev- 

 eral provinces of more or less importance may be recognized, chief 

 of which are : 



1. The estuary. 



2. The marginal lagoon. 



3. Epicontinental seas and mediterraneans. 



4. The ocean littoral. 



I. The Estuary. This is the point of meeting place of the 

 terrestrial and marine realms. It receives on the one hand the sedi- 

 ments and other material brought by the rivers from the land, and 

 on the other it admits the waters of the sea, which for a time at 

 least modify the character of the deposit. Alternately the waters of 

 the land and of the sea predominate, as a result of which the de- 

 posits formed in the estuary will have characteristics typical of both. 

 As a good example, we may consider the estuary of the La Plata in 

 South America. This has a length of 125 miles, and receives the 

 water of the Parafia and Uruguay rivers. The currents of these 

 rivers thus come into periodic contention with the tides from the 

 Atlantic. ( Willis-105 :-/p/.) Where the power of the tidal wave 

 balances that of the rivers, no current exists, a condition which may 

 continue for hours. (Revy-8i : <?p, 50.) Here at from 10 to 20 

 miles above the mouth of the estuary, the material held in sus- 

 pension is dropped, as a result of which submerged banks are form- 

 ing, which eventually grow into islands. The current during both 

 flood and ebb tide is swifter in the deep channels than in shallow 

 portions of the estuary, hence deposits made during flood tide will 

 be more copious over the shallows than in the deeper channels. 



