Situation of Zones without Rain, and of Deserts. 79 
leras, so that they can no longer cause rain to descend on 
the plains of Peru, whereas the heights are exposed almost 
every day to alternations of serene and cloudy weather, and 
to frequent storms. 
These causes will doubtless appear sufficient to explain 
the extension of absolute droughts; but it presents in the 
details a peculiarity worthy of attention. Although it may be 
said in a general manner that it never rains at Lima, or at 
least that there are never rains of large drops, we must, never- 
theless, remark, that, during a great portion of the year, the 
serene atmosphere loses its transparency, becomes troubled, 
and is covered by a singular vapour, known to the inhabi- 
tants under the name of garrua, garroua, or garruva, denomi- 
nations which are also applicable to mild rains of short dura- 
tion, as well as to the very small rains which occur in 33° N., 
between California and the Galapagos Islands. Whatever 
may be the different acceptations of this term, the vapours 
of the garrua of Limaare so thick, that the sun seen through 
them with the naked eye assumes the appearance of the 
moon’s disc. They commence in the morning, and extend 
over the plains in the form of refreshing fogs, which disap- 
pear soon after mid-day, and are followed by heavy dews 
which are precipitated during the night. At other times, 
and especially during the winter season, they rise like clouds 
to the height of the mountains of the coast, which they 
moisten sufficiently to allow of vegetation in places not much 
exposed to the heat of the sun; lastly, they become con- 
verted into more or less violent rains on the flanks of the 
Cordilleras, at a distance of fifteen or twenty leagues inland, 
where it becomes possible to obtain harvests. These rains 
prevail there from December till May, that is to say, during 
the epoch of the sun’s passing the zenith of that hemisphere, 
so that they coincide with those which present themselves 
generally between the tropic of Capricorn and the equator, 
and the phenomena have their normal arrangement, which 
is the reverse of the seasons of Valparaiso and of Cobija. 
This local effect of the garrua of Lima may be explained, 
as we have already stated, by the greater proximity of the 
Cordilleras, which there produce a remarkable freshness, 
