or SANTO DOMINGiO. ' 117 



miles along the top of a ridge, a distance that should have been made in three hours 

 easily in reasonably open ground. 



Thronghont the entire distance from Humnnneu, the rock is a gray syenite, so 

 uniform in character and appearance that one hard specimen would almost seem as a 

 sample of the whole. It is usually of a light color, moderately coarse grain and with 

 the hornblende in small crystals. No mica was noticed anywhere. T have been 

 thus detailed in the "personal narrative" of this particular journey for the purpose 

 of conveying a clearer idea of the character of the higher interior mountains of the 

 Island, and to show that moimtaineering in Santo Domingo, though not dangerous, 

 is quite as difficult as climbing over snow fields. 



From Humunucu, a trail crosses a comparatively low ridge, also in the same 

 syenite throughout, and strikes the Yaqui again, just opposite Jarabacoa. 



Returning again to Tabera, Avhence we started, we find the highly uptilted sierra 

 slates are overlaid by dark gray sandstones, with occasional pebble beds belonging 

 to the extreme base of the Miocene. This Miocene, though much disturbed, is 

 decidedly unconformable with the underl^dng Cretaceous. They are slightly meta- 

 morphosed so far as to show signs of alteration, but not sufficiently to lose their 

 sandy structure. The most marked effect of the metamorj^hic action is visible in 

 their stratification. The river bluffs are here very high and abrupt, and one section, 

 about half a mile from the house of Col. Placencio, shows an amount of contoi'tion 

 nowhere else observed in the Dominican Tertiary. The alteration of the sand and 

 pebble-beds is visible along the same line of strike for a distance of three or foiu- 

 miles to the westward, and the strata, which usually dip at high angles to the north, 

 vary in their strike all of the way from IST. W. to N". 20° W., the former being 

 about the normal direction. These are the " secondary rocks (perhaps of the Car- 

 boniferous system), which consist of dark sandstone flags, alternating with black 

 bituminous shales in narrow seams, dip X.N.E. < 33°. The rock is usually a dark 

 gray sandstone, and where the southern road from Santiago to San Jose de las JNIatas 

 crosses the Bao River, it is a conglomerate of the same, color, with a calcareous 

 cement, and dips as high as 50°. From the top of the hill west of the Bao, the 

 succession of strata can be seen almost uninterruptedly to the steep bluffs on the 

 Yaqui at Angostura. The dip gradually becomes lower, until at the latter place it 

 is nearly horizontal, varying from 5° to 10° from north to south along the extent of 

 the exposure, and at Santiago, still farther north, is reversed, dipping at a low ang!e 

 to the south. 



* Heiicken, Quart. Journ. Geo. Soc, \o]. x., p. 12". 

 A. P. S. VOL. XV. 2d. 



