38 
The sand-bank of the Boca Barra, however, may be attribu¬ 
ted to another and more powerful cause. The river Tehuan¬ 
tepec flowed not many years ago into the western lower la¬ 
goon, as may be seen by the map of the southern division of 
the isthmus. The opposing currents of both rivers destroyed 
reciprocally their strength, and caused the deposit in that par¬ 
ticular spot of the matter they bring with them. Fortunately 
the river Tehuantepec spontaneously abandoned this direction, 
and care should be taken to preserve it in the course which it 
has now adopted. 
Taking advantage of a calm, between two tides, Messrs. Ro¬ 
bles and Guido succeeded in going out to sea through the Bo¬ 
ca Barra, and executing the soundings indicated in the plans. 
They found that immediately after passing the bank there is a 
channel, the depth of which, even in the shallowest part, is of 
nearly 19f feet, this depth increasing afterwards rapidly. 
The exploring party concluded operations in this part of the 
isthmus, and returned shortly afterwards to San Dionisio. 
The party assembled at Juchitan towards the end of Octo¬ 
ber. This spot proving to be the centre of several trigono¬ 
metrical operations had been selected for the purpose of refer¬ 
ring to it the position of all the other points, after having 
previously ascertained its exact latitude and longitude. 
The season being now sufficiently advanced the exploring par¬ 
ty was divided into two sections, one of which was entrusted to 
Captain Robles, in whose abilities complete reliance could be 
placed. This section established themselves in the Yenta de 
Chicapa, which from that moment became the meeting point 
of the Commission until the close of their labours in the 
isthmus. 
Mr. Moro and his party proceeded northward, passing 
through Chivela, Guichicovi, and Boca de Monte. Guichi- 
covi is situated at the commencement of the rugged part 
of the sierra; and the gentle hills in the neighbourhood of 
Chivela, approaching this spot, are, at intervals, interrupted 
by precipitous ravines, through which several rivers and streams 
find a passage for their waters. The surface of the ground be¬ 
comes more level receding from Guichicovi towards Boca de 
