12S MiSCELtANEA. 



rous crj^stals of sulphate of lime from one to three inches in length. 

 M. d'Orbigny states that some of these crystals are acicular, and 

 more than even nine inches in length, others are macled and of 

 great purity ; those I found all contained some sand in the centre. 

 As the black and fetid sand overlies the gravel, and that overlies 

 the regular tertiary strata, I think there can be no doubt that these 

 remarkable crystals of sulphate of lime have been deposited from 

 the waters of the lake. The inhabitants call the crystals of selenite 

 padre del sal, and those of the sulphate of soda madre del sal ; they 

 assured me that both are found under the same circumstances in 

 several of the neighbouring salinas, and that the sulphate of soda is 

 annually dissolved and is always crystallized before the common 

 salt on the muddy bottom. The association of gypsum and salt in 

 this case appears to me interesting, considering how generally these 

 substances are associated in the older stratified formations. 



Mr. Reeks has analysed for me some of the salt from the salina 

 near the Rio Negro : he finds it composed entirely of chloride of 

 sodium, with the exception of 0*26 of sulphate of lime and 0*22 of 

 earthy matter; there are no traces of iodic salts. Some salt from 

 the salina Chiquitos in the Pampean formation is equally pure. 



With respect to the origin of salt in the salinas, the foregoing 

 analysis seems opposed to the view entertained by M. d'Orbigny 

 and others, and which seems so probable, considering the recent 

 elevation of this line of coast, namely, that it is due to the evapora- 

 tion of sea-water and to the drainage from the surrounding strata 

 impregnated with sea-salt. I was informed (I know not whether 

 accurately) that on the northern side of the salina, on the Rio Ne- 

 gro, there is a small brine-spring which flows at all times of the 

 year; if this be so, the salt in this case at least is probably of sub- 

 terranean origin. It appears at first very singular that fresh water 

 can often be procured in wells, and is sometimes found in small 

 lakes, quite close to these salinas. I am not aware that this fact 

 bears particularly on the origin of the salt, but perhaps it is rather 

 opposed to the view of the salt having been washed out of the sur- 

 rounding superficial strata, but not to its having been the residue of 

 sea-water left in depressions as the land was slowly elevated. — Dar- 

 win's South America, 1846, pp. 72-75. 



II. On the Chemical Composition o/* Calcareous Corals. 

 To the Editor of the Quarterly/ Journal of the Geological Society, 



Yale College Laboratory, September 26, 1846. 

 Sir, — In No. 7 of the Geological Journal (Part ii. p. 94-) there is a 

 short anonymous paragraph quoted " from Silliman's Journal," " On 

 the Chemical Constitution of Calcareous Corals," in which certain 

 analyses by the writer are cited, as supporting the remarkable 

 statement "that the Zoophytes which form these stony skeletons 



