330 REPORT OF NATIONAL MUSEUM, 1892. 



The terms lagoons and bays as here used are applied to such par- 

 tially landlocked bodies of water as now exist along oceanic borders 

 but which are often, at least in part, of less than marine saltness be- 

 cause of inflowing streams. The restricted use in this essay of the 

 terms lake and inland sea is indicated in the following paragraphs: 



In accordance with the elementary nature of these remarks it is 

 thought desirable to briefly characterize the various kinds of existing 

 bodies of water in which sediments similar to those which constitute 

 the various sedimentary formations are now in process of deposition. 

 Such a characterization is made to consist in part of an explanation of 

 the special terms just referred to. 



The term lake is properly applied, and ought to be restricted, to in- 

 land bodies of fresh water. It will be so used in this essay except 

 in those cases where a contrary practice has resulted in a public recog- 

 nition of such proper names as Great Salt lake, etc. 



The source of the water supply of lakes is rainfall, which is drained 

 into them from the surrounding land. It is therefore fresh in the ordi- 

 nary acceptation of that term, but as it enters the lake it always con- 

 tains at least a minute proportion of soluble salts derived from their 

 original home, the land, by leaching. The amount of salts in such 

 cases being inappreciable by gustatory test, lacustrine waters are prop 

 erly designated as fresh, but to remain fresh a lake must have free out- 

 flow and not excessive evaporation from its surface. Otherwise it will 

 become distinctly saline by the gradual accumulation of soluble salts 

 which inflowing streams constantly bring from the land. 



The term inland sea, as used in connection with the terms indicating 

 other bodies of water and with reference to certain formations with 

 which the geologist sometimes has to deal, is applied to any body of 

 water more or less completely surrounded by land which holds in solu- 

 tion a sufficient proportion of saline matter to modify or characterize 

 its aquatic fauna, or which holds a so much greater proportion as to be 

 sufficient to prevent the existence in it of such a fauna. Therefore an 

 inland sea, especially one that has an outlet, differs physically from a 

 lake only by the presence of at least a readily appreciable amount of 

 soluble salts in its waters. This restricted use of the term sea is war- 

 ranted by prevalent custom with reference to the Black, Caspian, Dead, 

 and other existing seas. 



While the difference between inland seas and lakes is important as 

 regards their respective aquatic faunas the distinguishing character of 

 both is subject to change because in both cases it depends upon physi- 

 cal conditions the stability of which is uncertain, and because any con- 

 siderable change of those conditions will result in a change of charac- 

 ter. For example such a change in the physical conditions which sur- 

 round a lake as would reduce the proportion of outflow to influx of 

 water and increase evaporation from its surface would, according to 

 the definition just given, change it to an inland sea. That is, soluble 



