314 ; CARTHAGENA. 
him to ascertain the astronomical position of several 
places which it was of importance to determine. 
During the six days of their stay at Carthagena, 
they made excursions in the neighbourhood, more 
especially in the direction of the Boca Grande, and 
the hill of Popa, which commands the town. The 
port or bay is nearly eleven miles and a half long. 
The small island of Tierra Bomba, at its two extre- 
mities, which approach, the one to a neck of land 
from the continent, the other to a cape of the isle 
of Bani, forms the only entrance to the harbour. 
One of these, named Boca Grande, has been arti- 
ficially closed, for the defence of the town, in conse- 
quence of an attack attended with partial success © 
made by Admiral Vernon in 1741. The extent of the 
work was 2640 varas, or 2446 yards, and as the water 
was from 16 to 20 feet deep, a wall or dike of stone, 
from 16 to 21 feet high, was raised on piles. The 
other opening, the Boca Chica, is from 36 to 38 yards 
broad, but is daily becoming narrower, while the 
currents acting upon the Boca Grande have opened 
a breach in it, which they are continually extending. © 
The insalubrity of Carthagena, which has been 
exaggerated, varies with the state of the great 
marshes that surround it. The Cienega de Tesca, 
which is upwards of eighteen miles in length, com- 
municates with the ocean ; and, when in dry years — 
the salt water does not cover the whole plain, the 
exhalations that rise from it during the heat of the 
day become extremely pernicious. The hilly ground 
in the neighbourhood of the town is of limestone, 
containing petrifactions, and is covered by a gloomy 
vegetation of cactus, Jatropha gossyptfolia, croton, 
and mimosa. While the travellers were searching 
a 
