42 
might be considered the minimum of their quantity, and they 
are always exceedingly clear and pure. 
This satisfactory result induced Sr. Moro to undertake with- 
out loss of time the inspection of the hill of Convento, in order 
to judge of the magnitude of the difficulties that might offer in 
that quarter. 
In that part where the hill of Convento is most depressed, 
namely, the northern side, the river Monetza takes its source, 
and following along a dale in the centre of the hill itself, 
penetrates under it, and crossing it entirely, comes out in the 
small valley in which it runs to San Miguel. The point of 
the opening in which the river has its origin is entirely hollow, 
since the gush of water which forms it, issues from the walls 
of a cave or fissure about 23 feet high, and the thickness of its 
vault is perhaps another 3 feet. Besides, the situation of the 
hill and the rock of which it is composed, which being of pure 
marble is admirably calculated to procure beautiful building 
materials as well as excellent lime to cement them, are all in- 
viting circumstances to convert it into a quarry ; thus, even 
were it considered necessary to make a cut' in this part of the 
hill, the work would be accomplished wliilst opening the 
quarry to procure the necessary materials. 
The river Monetza in running under the Cerro del Convento 
has only to cross a distance of about a hundred and ten yards, 
although it passes through the very centre, and consequently the 
thickest part of the mountain. 
Another barometrical level obtained froin observ^ations per- 
formed simultaneously at Tarifa and at the source of the 
Monetza showed that the level of this river is nearly the same 
as the stream adjoining Tarifa, the waters of which run to the 
Coatzacoalcos. The ground that lies between Tarifa and the 
source of the Monetza although level, is now and then inter- 
sected by torrent streams, the waters of which flow into the 
Monetza ; and as these streams have their origin at a short dis- 
tance from Tarifa, this ought to be considered as the proper 
spot for the division of the waters in the canal. 
The houses of Tarifa are somewhat elevated in tlie midst of 
