104 



oles to go as far as Bocoyna on the head waters of the Rio Oonchos, whe- 

 re there is a small settlement of Mexicans and Indians. Prom this place 

 onwards one must travel mounted or on foot. The highest part of the ran- 

 ge in this neighbourhood is Rumeraehic, 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. Mam- 

 mals 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 dry season to make tho murmuring accompaniment ono 

 always hears in the Alps, and as no breath of wind disturbs the constant 

 calm of the air, there is an absolute silence in the forest which is very im- 

 pressive; even the footfalls of one's own mules are deadened by the carpet 

 of pine-needles. 



These mesas are composed of almost level sheets of lightcoloured tra- 

 chyte, and beds of white friable volcanic ash, with local layers of white 

 pumi/* ^crustations of red and white chalcedony, and crystals of celes- 

 tine are also commonly seen. 



The commencement of the arroyos which feed the Fuerte river is 

 usually a basin-like space of bare stone completely denuded of all soil, 

 and without vegetation; the sides are steep, and the hollows soon plunge 

 down to the depths of the great canons; they remind one of the streams 

 on the peat-covered Irish hills, Kippure for example, where a furrow in 

 the living fibrous covering of heather and other plants, soon widens into 

 a gully in the soft peat. Though the scale of the phenomena is very" Af- 

 ferent, yet the forest on the mesa seems to play the part of the heather 

 on the peat, and prevent denudation of the underlying material. In tho 

 basins and valleys there are often rounded bosses, and sometimes high pi- 

 llars left standing in isolated positions, or in groups; they appear to be pro 

 duced by the protection afforded by hard, resistant patches in the trachy- 

 te; but, unlike ordinary earth piilars, do not develop into symmetrical 

 conical forms; being always twisted into strange and odd shapes, and so- 

 metimes overhanging considerably; some are more than 100 feet high. Be- 

 sides the summer rains, which are not heavy at elevations of seven or 

 eight thousand feet, there is a winter snowfall of about two feet, and the 

 greater part of this, probably finds its way through the surface soil, and, 

 by subterranean passages of the fissured rocks, to the water-level at the 

 bottom of the gorges; for in early summer the small streams are quite dry, 

 though there is plenty of water far down in the gorges. The most striking 



