Doyitr—Rio del Fuerte of W. Mexico, and its Tributaries. 6} 
country composed of weathered dark volcanic rocks, and studded 
with abrupt hills which rise like islands in a stormy sea of lava. 
There is little surface soil, and, except in a few shallow valleys 
like that of Sta Isavel, the region, owing to drought, is a desert. 
After reaching Cusihuiriachic, a town depending on very ancient 
and rich silver and lead mines, the llanos are seen stretching 
upward toward the watershed of the continent; they are very 
smooth, broken by few arroyos, and covered with grass forming a 
good cattle country wherever water is obtainable. Thirty miles 
to the N.W. of the town is a group of rocky hills whence streams 
flow in three directions—south-east to the Rio Conchos, which joins 
the Rio Grande del Norte, and discharges into the Gulf of Mexico 
—north to the Rio de Sta Maria, an inland system of drainage 
ending in a salt lagoon near the United States frontier—and west 
through the mountains to the Gulf of California. 
The anos preserve the original slope and surface of the old 
lava flows, and are protected from denudation by their lofty ele- 
vation, the small rainfall on the inland side of the mountains, 
and by a coating of soil with permanent grass.!. Travelling over 
them, is a pleasing contrast to progress over the stony plain, and 
the antique-looking, leather-slung coaches drawn by teams of eight 
or ten, well-matched, closely-clipped, white mules go at a fast 
canter over the smooth surface. ‘Towards the summit of the slope 
rounded hills studded with dwarf oaks appear, and the ground is 
broken ; but some attempt at grading the tracks enables wheeled 
vehicles to go as far as Bocoyna on the head waters of the Rio 
Conchos, where there is a small settlement of Mexicans and 
Indians. From this place onwards one must travel mounted or 
on foot. The highest part of the range in this neighbourhood is 
Rumerachic, a rounded mountain about 9700 feet above the sea. 
Here we enter on the pine-clad mesa, which extends, uniform 
and monotonous, in a belt 50 miles wide, along the crest of the 
Sierra; except in a narrow central ridge, the general surface is 
quite level, and covered by a sparse forest of small pines, with very 
little other vegetable life. Mammals and insects are alike unseen, 
and the only winged creatures are an occasional flock of ‘ blue 
birds ” or a stray woodpecker. There being no streams during the 
1There are also alluvial deposits in this region, containing bone remains of 
Quaternary age. 
