108 



sed by volcanic eruptions in the previous river valley damming the chan- 

 nel up with lava and ash; and when largest, the lake covered 100 square 

 miles, to a maximum depth of at least 1000 feet; the thickness of the la- 

 custrine strata below the present river level could not be ascertame wit- 

 hout boring. 



Should it ever be desired to regulate the flow of the Puerto river, 

 either for water-power or tor extended irrigation in the low country, it 

 could be done efficiently at a moderate cost, by constructing a dam at the 

 gorge of Kealito, where there is a narrow passage, solid rock for founda- 

 tion, and a long gentle slope for the reservoir. 



Above Tubares, low cliffs close in again on the river; here they are 

 of a compact white stone, in appearance like limestone, but probably de- 

 rived from the waste of the acid lavas; then the valley opens again as the 

 junction with the Urique river is reached, the left branch being the pro- 

 duct of the main stream from El Zapori and the Batopilas river. 



Long ages elapsed between the eruptions that built up the mesa, and 

 those which formed the Kealito group of foot-lulls; for during that inter- 

 val' the Urique and other rivers eroded valleys more than 5000 feet deep, 

 and extended the littoral plain at the expense of the plateau. After the 

 new volcanoes had covered the plain, the rivers deposited the lacustrine 

 beds of Tubares, and cut a deep channel through the erupted material. 



All the foothills are covered with a low forest of thorny trees and 

 shrubs, leafless in March, but not without blossoms, the "palo bianco" in 

 particular being covered with corymbs of large, white, sweet-scented flo- 

 wers the food of parrots and deer, and the haunt of humming-birds. A ye- 

 llow 'variety of the same species is common, and two trees produce large 

 clusters of rhododendron-like blossoms, pink and yellow respectively; log- 

 wood of small size is abundant, being used for fuel and for stakes. The 

 commonest large cactus is the pitahaya a clustering group of dark green 

 cylinders about 10 feet high, furnished with grey woolly hair near the top, 

 and like all the genus, with chevaux defrise of slender sharp spines. The- 

 re are large echinocacti which are eaten greedily by deer, whenever they 

 can penetrate the defensive armour of spines and hooks. The smaller ma- 

 miliaria with brilliant starry flowers were not generally in bloom in March. 

 Besides the perennial woody; or fleshy and fibrous plants, there is a nu- 

 merous and beautiful flora of herbaceous varieties that spring up on the 

 advent of the rains, and many of them are peculiar to this part of the 

 country; it has been only partially worked out, and there are probably ma- 

 ny kinds yet undescribed. All the shrubby vegetation is much more lu- 

 xuriant on the recent volcanic area than on the eroded spurs of the mesa. 



Proceeding now, from the junction of the Urique river, a new series 



