1G4 



ON THE TOPOflKAl'HV AND GEOLOGY 



gradually fshade into the bluish shales of the valley in exactly the same manner as the 

 change takes place in the centre of the valley, and the lower part of these blue shales 

 bear occasional beds of sandstone, probably on the same horizon as those near the 

 mouth of the canon north of Moca, or those near Limon on the road to Puerto Plata. 

 The mountain gi\e:< on a small scale, that is, with all of the members considerably 

 thinned out, a section from the top, nearly three-fourths of the way to the base of the 

 formation. The little island lying in front of the bay of Monte Cristi, called Cayo 

 Publico, is made up of the upper part of the shale series, and both there and in the 

 mountain itself we collected casts of corals and a few familiar mollusca, but all in a 

 poor state of presei'vation. 



The barren character of the Monte Cristi chain and the almost entire absence of 

 human occupation, with the consequent scarcity of roads, combined with the fact that 

 in this part of the range no results of economic value could possibly be hoped for, 

 prevented me from devoting any further attention to it than sending through it a 

 topographical pai'ty to make a hasty reconnoisance. Mr. Runnebaum obtained its 

 pi'incipal features by a rapid triangulation, and reported to me that the only rocks he 

 encountered were the shales and limestones of the upper part of the Miocene series. 

 His limited experience, however, did not permit him to make observations of the 

 details of structure sufhciently accurate to record here. 



1 myself followed its southern base in the valley several times, studying it from a 

 distance, and have examined its northern face in the same manner from the prominent 

 jjoint at the mouth of the Isabella, which commands a view almost to Monte Cristi. 

 Judging from the very imperfect data thus fuinished, fiom its diminished height and 

 width as well as from the structure of the hill of Monte Cristi and from Avhat infor- 

 mation Mr. Runnebaum was able to give me, it is probable that only the upper 

 members of the formation occur there, and that the anioiuit of disturbance has been 

 comparatively limited. Mr. Runnebaum found it in the main a dr}' barren series of 

 hills badly watered, but with a few little fertile spots where the natural irrigaticm 

 supplied the deficiency of i-ain. The coast is almost impassable on account of 

 thickets, mangrove-swamjjs, and quicksands, and he was obliged to go from Monte 

 Cristi to Estero Balsa in a boat in consequence of his inability to foj'ce his way 

 through the thorny brash over the hills. The bad trail from Guayubin to Estero 

 Balsa is the only road across the range between Monte Cristi and the Isabella Pass. 

 From this another trail branches off at Tiburcio in a central valley and runs east, 

 uniting with the latter route, and is sometimes used by the people of Gucn}'ubin in 

 going to or from Puerto Plata. 



