IGO 
GEOLOGY AND MINERALOGY. 
the line examined ; but of these and other erupted or basaltic 
minerals there is a great abundance. Immediately south and 
west of San Jose, and following up the course of the rivers, the 
ground is composed of fine alluvial clay, which reaches to the 
foot of the mountains. This clay is auriferous, and has been 
previously alluded to. 
Notwithstanding the chain of successive low hills which alters 
the horizontality of the northern plains, that alteration does 
not affect the general gradual slope of the land into the Gulf. 
The strike of these hills being generally N. W. and S. E., the 
southern extremity is more elevated than the northern, and the 
long back, or more gentle slope of the hills, is towards the 
Gulf. Again ; the more remote from the Sierra, the less eleva- 
ted the upheavals constituting the hills ; and from the configura- 
tion of the Gulf coast, no hill-range exists at the mouth of the 
Coatzacoalcos under water. The above considerations, as well as 
actual observation of the river, would lead to the presumption 
that the bar of the river is not a rocky obstruction, but an accu- 
mulation of sand and detritus from the river. 
Although muriate of soda does not exist in beds over the 
Isthmus, yet its great abundance on the surface justifies our 
notice of it under the geological description. Solar evaporation 
of the lagoons on the Pacific shore every year furnishes a large 
amount of a coarsely crystallized granular salt, which forms a 
crust on the margins of the lagoons to the depth of two or three 
inches. The same occurrence is common on the Gulf shore. 
The purification of the salt is simple and inexpensive, and when 
carried out on a large scale is profitable to the manufacturer. 
The country is admirably adapted to the manufacture of salt by 
art : nothing more being necessary along the coast and lagoons 
than to convey the water in a stream, and allow it to trickle 
over shrubs and branches of trees laid horizontally, when, from 
the excessive heat of the sun, most of the water would evaporate, 
and the salt crystallize on the twigs. By re-crystallization, the 
finer salt is obtained. Nature has pointed out this Isthmus as a 
locality where this manufacture might be carried on as a staple 
article of trade. 
The low average elevation of the mainland of the Isthmus 
