THE NITRATE DEPOSITS OF CHILE 21 



certain forms of seaweed or kelp. Iodine is taken up by such plants 

 from the sea water and fixed in their tissues. 



The iodine may, therefore, have come either from sources on the 

 land or in the water or both. As yet no strong evidence has been 

 produced to show that it came from the land. On the other hand, 

 we have no definite evidence that it came from marine sources, but 

 at the same time we know that the pampa was formerly probably 

 covered by a body of sea water, at first connected with the open ocean 

 and later cut off from it. During the time that it was more or less 

 directly connected with the ocean an immense accumulation of 

 iodine-bearing marine plants may have grown there, gradually 

 collecting the iodine not only from the limited quantity of water 

 represented by the arm of the sea in which the plants grew, but also 

 from a constant fresh supply of sea water circulating in and out 

 from the ocean, or dashed over a possible dividing barrier during 

 storms and high tides. Possibly also similar marine plants from the 

 open ocean may have come in with this sea water and accumulated, 

 in a manner similar to that seen in many parts of the world today, thus 

 augmenting the marine plants already growing there. After the 

 region had been completely cut off from the ocean and desiccation 

 had progressed sufficiently, this marine flora would decay and thus 

 afford a great quantity of iodine. The simple evaporation of the 

 water of the inclosed basin would of course account for some of the 

 iodine, as this material is universally present in sea water, but in 

 quantities so extremely minute that it seems necessary to suppose 

 that the iodine of the pampa has been segregated from far larger 

 quantities of water than those of the basin alone. 



Hence, though the possibihty of the source of the iodine from the 

 decay of iodine-bearing minerals or springs on the land cannot be 

 denied, yet the facts at hand suggest more strongly a source from 

 marine plants. 



As regards the borates found in the pampa, it may be said that, 

 like the borates found under similar conditions in many other arid 

 regions, they were probably derived mostly from the decay of boron- 

 bearing minerals and from springs carrying boron compounds, such 

 as are common in many mountainous regions, and especially those 

 of igneous origin. Boron compounds occur also in sea water and 



