62 



ON THE TOPOGRAPHY AND GEOLOLGY 



of the Verde or Gi'een River, it crosses some more hills. Here, the Tertiary rocks 

 coming to the surface, the road is diy, and the soil usually shallow ; but immediately 

 afterwards, entering again the black loam region, there is a stretch called the 

 " Laguna Prieta" or " Black Lake," a mile or two of road which, during the entire 

 rainy season, fully merits the name. 



There is a marked dissimilarity in the vegetation of the eastern and western ends 

 of this valley, caused by the difference in the amount of moisture in the air, and the 

 difference in the rain-fall. The trade-winds from the Atlantic draw into the gap of 

 Samana Bay as into a funnel, and are conducted by the mountain chains, as between 

 two walls, directly down the valley, depositing their vapors, either as rain or dew, 

 over the eastern end, even too abundantly at first. But in their progress they 

 generally become drier, until just after passing Santiago there is a very appreciable 

 diminution in the rain-fall, and a consequent change in the character of the plants. 

 Within ten miles west of Santiago nearly all of the forest trees common in the Vega 

 disappear; Acacias of two or three species take their place, disputing the ground 

 with Cacti. Of the latter, one of the most conspicuous is an arborescent Opuntia with 

 a peculiarly flat, narrow leaf, often carrying this tendency to compression to the 

 extent of having its woody stem of a foot thick of" a long elliptical section. The 

 plant not rarely acquires a height of twenty feet, and occasionally one of twenty- 

 five feet high may be seen. Besides this, a columnar Cereus, rivalling it in height, 

 and very similar to one known In Lower California as " Pitahaya dulce,^^ Is equally 

 abundant. Two other species of Cereus, three or four of Opuntia., one Melocactas, a 

 little gregarious Mammillaria, and two or three climbing species of Cereus (?), make 

 up the list. It Is not to be understood that this change In vegetation Is abrupt. A 

 straggling little Opuntia or an occasional Cereus may be found even as far east as 

 Santiago, and the forest of the more eastern type clings to the damp spots along the 

 river botton almost to Guayubln ; but so marked Is the style of the plants away from 

 the river, that In the foot hills north of Guayacanes I could have Imagined myself 

 on the plains of Magdalena. ^forth of the Yaqul the road, very wide and very 

 level, runs nearly parallel with the river, rarely touching It, usually at the distance of 

 a mile or two, directly down the valley, through some very good land, now used for 

 grazing solely, and apparently barren, but which, properly Irrigated, could be made 

 to yield excellent, cro])s. It Is, howevei', so Inferior to other regions In the Republic 

 that the population must Increase many fold before such artificial aid will be resorted 

 to here. There Is another drawback which would doubtless have great Influence. 

 There are but few streams, and these are small, running out of the northern or Monte 



