OF SANTO DOMINGO. 



123 



ite, with no trace of mica, makes up the mass, while in another we found a coarse- 

 grained rock with large crystals of feldspar, and in place of hornblende a greenish 

 mineral, possibly chlorite. The mouth of the Jicome is in the outer or first belt of 

 Syenite; and here is repeated the material already mentioned at the crossing of the 

 Magna and elsewhere, a rock so peculiar as to be immediately recognized, although 

 here it has undergone a slight modification, in that the feldspar is white and some 

 parts of the mass are finer grained than usual. 



Abundant pi-oof exists of the oi'igin of the quartz veins here. They never show 

 well-defined walls, and whenever mica is found in the coimtry rock it is almost 

 always entangled in the quartz also. 



In the Cretaceous belt between the Jicome and Dajao the slate is all more or less 

 serpentinoid and of various shades of green and gray. In some cases it is nearly a 

 pure chlorite; and by following the same line of strike to Dajao it can be seen to 

 change gradually to a claystone varying in color through all the shades of black, 

 gray, green, brown and rusty. Some beds are almost identical with the rock from 

 the Bao and the Jagua, but everywhere it bears an abundance of cpiartz veins, not 

 infrequently stained with carbonates of copper. Although the Mao River, which 

 here takes a turn to the eastward, runs during that part of its course along the 

 centre of a synclinal axis ; the fact could only be ascertained by a detailed examination 

 of a much larger region than the immediate area in question. As has been demon- 

 strated above, the limestones of this part of the country overlie the conglomerates 

 and are in turn overlaid by the shale ; the whole having been pushed up by the syen- 

 ites which have found egress to the surface in nearly parallel east and west lines. 

 The stratification has been so nearly obliterated that only here and there, as in case 

 of the more compact limestones, can any dips be demonstrated. Both south and 

 north of Dajao there are intrusive belts. The southern appears within a couple of 

 miles of the settlement and extends more than half way to Pico Gallo. The northern 

 makes its appearance as 'a comparatively narrow strip on the ridge towards Guara- 

 guano, just after reaching the summit from the river. On the southern tlank of this 

 latter the limestone abounds without recognizable dip, and small outcrops of lime- 

 stone also occur a mile south of Dajao. Between the two limestone exposures the 

 country is a mass of clay and talcose-slates, whose principal characteristic is that 

 they all seem to be " on end," no exposure showing a dip that can be depended on for 

 measurement ; though the quartz veins and all other collateral signs that occur seem 

 to indicate a vertical position, or are approximately so. A full half of the width of 

 this synclinal axis is occupied by the Mao cailon, and there being no exposures on 



