LAGOONS OT? AEATA. 
185 
sandstone of Araya, I mean tlie muriatiferous clay. This 
clay, hardened, impregnated with petroleum, and mixed with 
lamellar and lenticular gypsum, is analogous to the salzthon, 
which in Europe accompanies the sal-gem of Berchtesgaden, 
and in South America that of Zipaquira. It is generally of 
a smoke-grey colour, earthy, and friable; but it encloses 
more solid masses of a blackish brown, of a schistose, and 
sometimes conchoidal fracture. These fragments, from six 
to eight inches long, hare an angular form. When they are 
very small, they give the clay a porphyroidal appearance. 
We find disseminated in it, as we have already observed 
either in nests or in small veins, selenite, and sometimes’ 
though seldom, fibrous gypsum. It is remarkable enough’ 
that this stratum of clay, as well as the banks of pure sal- 
gem and the salzthon in Europe, scarcely ever contains shells 
while the rocks adjacent exhibit them in great abundance. 
Although, the muriate of soda is not iound Adsible to the 
ej e in the clay of Araya, we cannot doubt of its existence. 
It shows itself in large crystals, if we sprinkle the mass 
with rain-water and expose it to the sun. The lagoon to the 
east ot the castle ot Santiago exhibits all the phenomena 
which have been observed in the salt lakes of Siberia, 
described by Lepeckin, Gmelin, and Pallas. This lagoon 
receives, however, only the rain-waters, which filter through 
the banks of clay, and unite at the lowest point of the pen- 
insula. While the lagoon served as a salt-work to the 
Spaniards and the Dutch, it did not communicate with the 
sea ; at present this communication has been interrupted 
anew, by faggots placed at the place where the waters of 
the ocean made an irruptionin 1726. After great droughts, 
crystallized and very pure muriate of soda, in. masses of three 
or four cubic feet, is still drawn from time to time from the 
bottom of the lagoon. The salt waters of the lake, exposed 
rests on a slate-clay, mixed with quartzose sand ; but there is no proof of 
the muriatiferous clay of the salt-works being of more ancient formation 
than this slate-clay, or of its alternating with banks of sandstone. No well 
having been dug^ in these countries, we can have no information respect- 
lng the superposition of the strata. The banks of calcareous sandstone, 
which are tonnd at the mouth of the salt lake, and near the fishermen's 
huts on the coast opposite Cape Macano, appeared to me to lie beueath 
the muriatiferous clay. 
