106 PROCEEDINGS OE THE SCIENTIFIC ASSOCIATION. 
of Port-of- Spain. It meanders through an extensive man- 
grove swamp which reaches close to the town. There is 
another extensive swamp at the mouth of the river Diego 
Martin, westwards of the western spur, and 4^ miles from 
the town. 
The above plain is sheltered E. to N.W. by the surround- 
ing mountains and hills : it is, however, open to the south- 
erly, but partly only to the S. E., S. W. and W. winds. 
The northerly wind is chilly. The easterly and south- 
easterly winds are cool and pleasant ; but having swept 
over the great Caroni swamp, they are saturated with marsh 
effluvia, as also the westerly and south-westerly winds, but 
to a much lesser extent. These and the southerly winds 
are hot, and th8 latter generally accompanied with heavy 
showers. That section of the plain which lies at the corner 
of the western spur and the range is exposed to the south- 
easterly winds ; and in the same manner is the portion, 
which lies at the corner of the eastern spur and the range, 
exposed to the south-westerly wind. And it is a fact that 
these two portions are less salubrious than the rest of the 
plain. 
The harbor of Port-of- Spain, which is exposed to the 
full force of the easterly breeze, may be said to be excep- 
tionally healthy, and this may be easily explained. When 
no obstacle occurs, marsh effluvia may be carried very far 
off by winds, and any intermediate level ground over which 
they sweep may remain comparatively healthy. But where 
the winds, carriers of the effluvia, meet with any obstacle, 
as, for instance, a range of mountains or high hills, then 
the effluvia accumulate on the flanks of those high grounds 
to a height of 600 to 800 feet which may thereby become 
uninhabitable. Of this we have a striking illustration at 
