108' 



sed by volcanic eruptions in the previous river valley damming tlie chaii- 

 nel up with lava and ash; and when lai-gest, the lake covered 100 square 

 miles, to a máximum depth of at least lUOO feet; the thickness of the la- 

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

 hout boring. 



Should it ever be desired to regúlate the flow of the Fuerte river, 

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

 coiüd be done eft'iciently at a modérate 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 Tubax'es, low clifl's cióse in again on the river; here they are 

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

 rived froin the waste of the acid lavas; then the valley ópens again as the 

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

 duct of the main stream f lom El Zapori and the Batopilas river. 



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

 those which formed the Üealito group of foot-hiUs; for duriug that inter- 

 val; the Urique and other rivers eroded valieys more than uüUÜ feet deep, 

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

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

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



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

 shrubs, leañess in March, but not without blossoms, the ' 'palo blanco" in 

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

 wers, the f ood of parro ts and deer, and the hauut of humming-birds. A ye- 

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

 clusters of rhododendi-on-iike blossoms, pink and yellow respectively; log- 

 wood of smaU size is abundant, being used for f uel and for stakes. The 

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

 cylinders about 10 feet high, f urnishejl with grey wooliy hair near the top, 

 and Iike all the genus, with chevaax de frise of siender sharp spines. The- 

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

 can penétrate the def ensive armour of spines and hooks. The smaller ma- 

 millaria with brilliant starry ñowers were not generally in bloom in March. 

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

 merous and beautif ul 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 área than on the eroded spurs of the mesa. 

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



