OF SAN^TO DOMINTGO, 



150 



south bank of the Camu Kiver, and is connected with Santiago by a road running 

 partly in the valley, partly over the hills back of the latter town. This road furnishes 

 some opportunities of examining the upper part of the formation, here a little peculiar 

 in that it contains an uimsual amount of sandstone. 



As has already been described, the bluffs under Santiago are composed entirely of the 

 blue shale, a cross-section of which is exhibited by the cutting of the Yaqui and a lesser 

 one by the arroyo of IN^ivaje. The suburb of ISTivaje on the south side of that creek 

 extends along the road towards la Yega, gradually rising on the flank of the hill. In 

 the village, but more especially just beyond it, beds of sandstone crop out in the bed 

 of the road and in the banks on each side, their dip being conformable with the 

 subjacent shale. In many places they show fine examples of ripple marks, and in one 

 instance I observed the peculiar surface called by D. D. Owen "mud furrows," 

 similar to the figures in the Report of Geological Survey of Iowa, Wisconsin, and 

 Minnesota, Table 1 D., fig. 1, though hardly so sharply defined. Some beds of the 

 usual yellow claystones occur, interstratified with the harder rock, and some of the 

 sandstone contains large pebbles. From this fact, as well as that the conglomerate 

 beds of Angostura lie above dark shale and below limestone, it follows as an almost 

 inevitable inference that those conglomerates are the equivalent of the yellow shale of 

 Guayubin. 



Very soon the sandstones become horizontal and even dip in the opposite direction, 

 and about two or three miles from Santiago they show only a surface in the road-bed 

 of a pebble-bearing calcareous sand seamed with soft streaks of lime. Bej^ond this 

 they disappear under a soil of black loam, so soft when wet as to well merit the name 

 of the " Laguua Prieta," or black lake, given to a couple of miles of road north of 

 Puiial Creek. Where the road crosses the bed of the creek the bluffs show small 

 outcrops of the brown shale so like the surface earth as to be hardly distinguishable. 

 In fact it is not improbable that the latter owes its origin in great part to the dis- 

 integration of the former. Its dip seems to be to. the northeast, though nearly 

 horizontal south (^f the Punal. The low hills of Caimitos, which unite Santo Cerro 

 with the higher hills on the Yerde, are made up in great part of a still higher set of 

 beds, here a yellowish-white calcareous claystone or marl, with a marked northern 

 dip ; and on the Rio Yerde itself, although the brown shales occur in the low bluffs 

 where the I'oad crosses it, the gravel in its bed contains corals like those from the 

 north face of the Samba Hills, and which have evidently been washed out of limestone 

 beds to the west. 



Up the Yerde from this ]ioint the section is not unlike a pai'tof that up the Yaqui. 



