;o2 Superficial Saline Deposits. part ie. 



Superficial Saline Deposits. 



This subject may be here conveniently treated of: 

 I will begin with the niosfc interesting case, namely, 

 the superficial saline beds near Iquique in Peru. The 

 porphyritic mountains on the coast rise abruptly to a 

 height of between 1,900 and 3,000 feet: between their 

 summits and an inland plain, on which the celebrated 

 deposit of nitrate of soda lies, there is a high undulatory 

 district, covered by a remarkable superficial saliferous 

 crust, chiefly composed of common salt, either in white, 

 hard, opaque nodules, or mingled with sand, in this 

 latter case forming a compact sandstone. This sali- 

 ferous superficial crust extends from the edge of the 

 coast-escarpment, over the whole face of the country ; 

 but never attains," as I am assured by Mr. Bollaert 

 (long resident here) any great thickness. Although a 

 very slight shower falls only at intervals of many years, 

 yet small funnel-shaped cavities show that the salt has 

 been iu some parts dissolved. 1 In several places I saw 

 large patches of sand, quite moist, owing to the quan- 

 tity of muriate of lime (as ascertained by Mr. T. Eeeks) 

 contained in them. From the compact salt-cemented 

 sand being either red. purplish, or yellow, according 

 to the colour of the rocky strata on which it rested, 

 I imagined that this substance had probably been 

 derived through common alluvial action from the lavers 

 of salt which occur interstratified in the surrounding 

 mountains : but from the interesting details given by 



1 It is singular how slowly, according to the observations of M. 

 Cordier on the salt -mountain of Cardona in Spain (' Ann. des Mines 

 Transl. of G-eolog. Mem.' by De la Beche, p. 60), salt is dissolved 

 where the amount of rain is supposed to be as much as 31*4 of an 

 inch in the year. It is calculated that only five feet in thickness is 

 dissolved in the course of a centurv. 



