144 



ON THE TOPOGRAPHY AND GEOLOGY 



halanced by the great number of streams to be crossed and by the sticky mud that 

 hardly ever dries, shaded as it is b}^ the dense forest. Rock exposures along the road 

 are very few and unsatisfactory, but, wherever found, they show invariably a shale, 

 magnesian or argillaceous and without detei-minable dij). ISTone of the limestone of 

 Hatillo was seen. 



Very different from this pass is the road that passes through Cevico and crosses 

 the Sillon de la Yiuda. After crossing some small savanas and rolling hills to the 

 arroyo Chaquey, with the usual red soil on all the hills, and occasional outcrops of 

 white and I'ed talcose slates and some sandstones it crosses a bold hill, the Loma de 

 los Palos. It has been observed that Mahogany is found only on calcareous soils, 

 and, although no limestone has ever been encountered on this road, there is quite an 

 extensive " mahogany cut " on the west side of this hill. I have never been able to 

 decide whether this is indicative of a little outcrop of Sierra limestone, or is, as is 

 more probably the case, due to the presence of an outline of Miocene sandstone, such 

 as is found a few miles further east. The latter theory is the most plausible. The 

 hill itself is quite stony, though few outci-ops occur except at its eastern base where 

 coarse sandstone blocks are quite numerous, although most of the little rock visible, 

 in place, is the soft shale so characteristic of this i-egion, and that differs but little 

 from the superposed clay in consistency. After passing a little beyond the base of 

 this hill, in the bed of the first stream, there is a good exposui'e of the highest mem- 

 ber of the Dominican Miocene, a light-colored limestone, lying horizontally on the 

 shales, amorphous, almost crystalline in appearance, though not in reality, and contain- 

 ing a few, but unmistakable, foraminifera — principally the little nummulite-like 

 fossil so useful everywhere else in identifying the formation, and which is found 

 throughout the formation from the blue shale to the to[) of the series. This commences 

 about three miles west of Cevico and continues uninterruptedly to a mile south. At 

 Cevico I detected in addition, corals and a few mollusca. After passing beyond the 

 region of Tertiary, Avhich extends back betwT^en the hills of the range like a bay, the 

 road rises gi-adually over a succession of low-rolling savanas to a point five miles 

 from the town where it enters the forest, and almost immediately begins to climb the 

 high spur of the Cuesta Blanca, or white I'idge ; the horse-trail winding between and 

 over, blocks of coarse sandstone, some of them two and three feet across. Just be- 

 yond the summit on the southern slope, where the ridge is but a few feet wide, the 

 trail is pinched so narrow that a horse can hardly squeeze through between the an- 

 gular masses of a couple of beds or dykes of a whitish rock, which gives its name 

 to the hill. I admit my inability to decide the character of this rock. Even under 



