88 



On the Fossils of the Eastern Portion 



[July 



and 2000 grains, evaporated at 212", gave a solid residue of of a grain, 

 the greater part of which consisted of muriate of soda with a little sul- 

 phate, and the remainder of carbonate of lime. The water of the well 

 below had nearly the same specific gravity-, but contained in 2000 grains, 

 one grain of solid matter, of which of a grain were soluble in water, 

 and contained muriate of soda and a little sulphuric acid and lime ; the 

 insoluble part consisted of carbonate of lime. Neither of the waters 

 contained any trace of alkaline carbonates or of magnesia. It is un- 

 necessary to go further into the analysis here, as another bottle of the 

 same water had a higher specific gravity, and contained more lime, a 

 circumstance sufficiently accounted for by the escape of a portion of the 

 carbonic acid from the other specimen. The water of the lake is clear, 

 and has no unpleasant smell ; but the mud at its bottom is strongly im- 

 pregnated with sulphuretted hydrogen. In February, 18j}4, when the 

 specimens were collected, the lake was in no place more than 5 feet in 

 depth of water and mud, but when full it may be eight or ten feet deep in 

 some parts. A layer of salt 2 or 3 inches thick covered the hoiiomunder 

 the mud, and when broken up and removed, was found to be composed of 

 a middle plate, with radiating laminae above, and having a striated ap- 

 pearance below. That obtained by diving and bringing up baskets of the 

 black mud, at a season when there was much more water in the lake*, 

 was also formed under the surface of the mud in lamellar spiculi radiat- 

 ing in every directionf. The salt accumulates slowly, and is collected 

 only once in several years, the quantity having diminished in consequence 

 of the mounds erected above the edge of the crater to regulate the supply 

 of water, having been neglected ; but it is evident, from the great beauty 

 of the specimens obtained, that the quality is not affected by this cause. 

 The salt is collected at the end of the dry season, when the water is low ; 

 and I observed mounds of the black mud on the banks, covered with an 

 efflorescence of tabular crystals. The salt is used for washing and dying 

 chintzes, &c., and is exported to considerable distances. I imagined that 

 the water of the lake in which such large quantities of salt were deposit- 

 ed, was saturated; but I found its specific gravity to be only 1 027*65, a 

 solution of the salt itself obtained from the bottom at the same time 

 being 1148-4 ; and the water rapidly dissolved the crystals thrown into 



* July, 1824. 



+ The natron of a lake near Maracaybo in South America occurs in the same %vay, the 

 Indians breaking up the layers of salt with long poles; and then, by diving, they re- 

 move it from under a bed of mud which covers it, and they place it in small canoes, as is 

 done at Louar. Journal of the Royal Institution, vol. i., p. 188. 



