Doyte—Rio del Fuerte of W. Mexico, and its Tributaries. 71 
purple, and rose predominate—and no such displays were seen 
by the author, since the wonderful sunsets caused by the eruption 
of Krakatoa. 
At San Blas there is a bar of rock across the stream; it is 
apparently metamorphic, and contains dark-red and green jaspery 
bands (specimen lost). Just above this place a very cold night 
was experienced, with dense fog—a surprising thing in the hot 
country, and the only fog seen by the author in Mexico. The ex- 
planation appears to be as follows:—On the mountain sides at night 
the clear air is chilled by the radiation of the ground; but, being 
too dry to deposit dew, falls a great deal in temperature, and 
slides into the bottom of the ravines. Here it is further chilled 
by radiation, and deposits copious dew; but, still cold, it runs 
rapidly down to the river and rolls on towards the sea. At San 
Blas it is checked by a line of low hills, and spreads out as a 
lake of cold, foggy air. It was observed that everything within 
about ten feet of the bottom of small arroyos was drenched 
with dew, while objects higher up were quite dry in the morning. 
As one proceeds towards the coast the plain becomes quite flat ; 
but hills of voleanic rock rise abruptly from it at wide intervals. 
The brown leafless forest of small trees gives way gradually to 
increasing numbers of cacti, especially a large variety of pilahaya, 
and twisted stvris, with poisonous thorns, which almost mimic a 
writhing knot of grey-green snakes. Where water is applied, the 
sandy plain is fertile; and the banks of the river, like a little 
Nile, are fringed by irrigation farms, where excellent cane for 
sugar, with oranges, bananas, and maize are raised. 
The margin of the water is alive with the bright plumage 
and songs of birds; but away from it, the plain is covered by 
groves of cacti, to the exclusion of everything else, and their 
clustering, green, leafless columns in endless succession, present a 
singular appearance. An attempt has been made to irrigate on a 
large scale, but only a small part of the immense cactus groves 
has been touched. The woody core of these plants contains tar, 
and yields on distillation a gas of high illuminating power. There 
isa road through the cacti to Topolobampo, a large landlocked 
bay which, on account of its possibilities as a harbour, has been 
carefully surveyed by the Hydrographic Department of the United 
States Government; their chart shows clearly that this was the old 
