832 THE POPULAR SCIENCE MONTHLY. 



cient seas. From among the numerous instances of this kind that 

 present themselves to my thought, I select three the mouths of the 

 Rhone, the Caspian Sea, and the Dead Sea. 



The map of the mouths of the Rhone shows that the lands for about 

 twenty miles from the Mediterranean are cut up by numerous lakes, 

 the principal of which, that of Valcares, exceeds sixty kilometres in 

 superficial area. These lakes have been formed by the action of the 

 alluvial contents of the river, which, being deposited on the bottom of 

 the sea, have raised bars inclosing bodies of water. The water within 

 the ponds, evaporating under the summer heat, is depressed in level. 

 If the ponds were wholly isolated from each other, and had no com- 

 munication with the sea, there would accumulate in each of them after 

 a time, varying with its depth, a deposit of gypsum, and above this 

 one of sea-salt, and so on through the series we have described ; and, 

 as the ponds are as a rule quite shallow, the saline deposits would all 

 be thin. Things, however, do not go on thus. Most of the ponds 

 communicate with each other and with the sea ; consequently, when 

 the water in them evaporates, the level is re-established with water 

 that comes from the sea. In this way a pond, the bottom of which is 

 only a few feet below the level of the sea, would become filled with 

 saline substances if the canal of communication did not become choked. 

 The Lake of Lavalduc, the surface of which is several yards below 

 that of the Mediterranean, is depositing gypsum. 



These facts show us saline deposits in process of formation under 

 our very eyes, and it is not at all necessary, in order to explain their 

 formation, to invoke changes of relief or any perturbations in the 

 crust of the globe, but only to take an exact account of the manner 

 in which a delta is formed, and of the circumstances that are a con- 

 sequence of that mode of formation ; and, although the delta of the 

 Rhone is not one of the most extensive of the deltas of the modern 

 period, it is one of the most remarkable and complete in respect to the 

 spontaneous formation of saline deposits. If we should go into details, 

 we should find a complete concordance between what is going on in 

 the delta of the Rhone and what has been revealed in the study of the 

 saliferous formations of past ages. Thus, saline deposits are forming 

 in these more or less wholly isolated ponds : we have, then, a saliferous 

 horizon in the delta of the Rhone, with the deposits generally sepa- 

 rated ; on the other hand, each of the deposits nearly always appears 

 of a lenticular form, because the ponds of the estuaries necessarily, 

 from the mode of their origin, assume that shape. The same principal 

 characteristics are presented by most of the beds existing in the sedi- 

 mentary deposits. 



If, now, by any incident, a pond which has been closed and has 

 deposited its gypsum is again brought into communication with the 

 sea, life will reappear in it, and mollusks will leave their shells on top 

 of the gypsum. If evaporation is resumed, life will disappear for a 



