20 R. A. F. PENROSE, JR. 



life in thie nitrates of Tarapaca, may be explained in a manner similar 

 to that suggested for the absence of guano, that is, the water became 

 too heavily charged with saline matter for such life to exist, and the 

 remnants of what had previously existed were gradually destroyed or 

 were covered up by later pampa deposits. 



If the nitrate was derived, as already described, from old guano 

 beds long since disintegrated and eroded, then we might expect to 

 find phosphates from the same source concentrated somewhere on 

 the pampa; but such, so far as known, is not the case, though of 

 course phosphates are found in the still existing later guano. Per- 

 haps, however, phosphates from the old eroded guano may exist, 

 and may not yet have been discovered, as the pampa has been but 

 little studied outside its nitrate deposits. As the phosphates in 

 guano are both soluble and insoluble, some of the former derived 

 from the old guano may possibly have percolated into the limestone 

 existing in parts of the region, forming insoluble calcium phosphate, 

 such as occurs in coral formations in the West Indies and the South 

 Sea Islands; while perhaps some of the insoluble phosphates result- 

 ing from the old guano may yet be found among the sediments of the 

 sea bottom which now forms the pampa. 



It is possible that in addition to the nitrate derived from guano, 

 a small amount of it may have been derived from the decay of the 

 marine and land vegetation of the interior basin. This decay would 

 set free nitrogenous vegetable materials from which nitrates might 

 have been formed, just as from guano. Nitrogen, however, is much 

 more abundant in guano than in vegetable matter, and, therefore, 

 the probability seems to be that guano was by far the more impor- 

 tant source of the nitrates. Marine vegetation, however, probably 

 played a most important part in supplying the iodine found in the 

 region. 



The source of the iodine in the nitrate and salt deposits of the 

 pampa has been a much-discussed subject. Iodine is a constitu- 

 ent of many minerals and is found in many mineral springs, as 

 well as in minute quantities in sea water. It also enters in small 

 but appreciable quantities into the composition of certain marine 

 plants and some sea animals. In fact before the iodine of Chile 

 came into use, most of the iodine of commerce was extracted from 



