158 



(.m TllK 'JVL'OOIIAl'UY AXD GEOLOGY 



that the yellow shale continues, and at Esperanza the Aveatherecl-out shells of Arca^ 

 Oyster, Venus, Cassis and S'pondylus, although mixed with surface pebbles, show 

 that their source cannot be far distant ; and Mr. Bonaczy reported to me the blue 

 shale at Ynamagado, south of the river and but a couple of miles distant, dipping- 

 north at a veiy low angle. 



From the little hill, hardly more than a roll in the plain, near Esperanza, and just 

 off the road, one of the finest views in the valley can be obtained. The valley is so 

 level that the hill commands a pi'ospect over evei'ything both east and west, while 

 there is probably hardly a better spot in the whole region from which to see the high 

 central mountains. It is directly in front of the Kucillo, and the whole range can be 

 taken in at one view. . .. 



From Esperanza to Santiago but one or two trifling little exposures occur, and 

 there, while showing a little more sandstone in the shale and a little more undulation 

 in the beds than further west, give us no additional facts. The whole valley, from 

 Santiago to Monte Cristi, and from side to side, is made up entirely and only of 

 Miocene strata, and usually the more modern parts only of these beds can be seen in 

 the valley, except where the rivers have cut through the Samba Hills. I make this 

 categorical statement as a summary, because it has been asserted to be otherwise.* 



Santiago lies at about the highest point of the valley, at a height carefull}^ 

 ascertained by barometer of 570 feet above the sea. It lies between the Yaqui and 

 the base of a range of low hills which project from the south and nearly divide the 

 valley into two parts. The water-shed betAveen the streams emptying into the 

 Yaqui and the Yuna is formed in part by these hills and in part by the nearly level 

 parts of the valley north of them. Two roads iiin out from Santiago eastward, con- 

 necting it with Moca. The most northern running in the valley is entirely on level 

 ground, hardly an outcrop being visible over its entire length. South of it a more 

 direct route cuts across the hills, separating from the Yega road a mile southeast of 

 the town. Along the former route, wherever rocks were observed they alwa^^s proved 

 to 1)e a rather loose-grained, soft, shaly sandstone, the equivalent of the Guayubin 

 shale, but more sand}', and not unlike some beds observed on the Canna River. 

 Fossils were not detected, but its stratagraphical position above the blue shale is 

 indisputable. In some places near the northern hills an argillaceous limestone 

 appears. The dip is indifferently both north and south and constantly vai'ies, but 

 never rises higher than 8° or 10°. 



La Yega lies close to the foot-hills of the Sierra in a beautiful flat plain on the 



. v.. * llcuekeii. (^liait. Joiuii. Gcolog. Soc, London, 18ij3, p. 115, et seq. 



