OF SANTO DOMINGO. 



1G7 



gray shales with mtercalated strata of sandstone helonging to the lower part of the 

 blue shale series. This upheaval is not extensive and the base of the outcrop near 

 Piedra Gorda shows a marked curve, the beginning of a synclinal axis. J^ear Lima 

 I found a dark gray conglomerate with broken fragments of shell very similar to the 

 conglomerate bed of the Angostura of the Yaqui ; but directly on commencing the 

 ascent of the hill the brown shale of Guayubin appears, and dipping to the south 

 extends to the top of the pass. ISTear the summit the higher hills on both sides are 

 seen to be capped with the usual white limestone, apparently nearly horizontal ; but 

 it is not encountered anywhere on this part of the road. In the shale ascending the 

 south side of the hill near the summit, although fossils were nowhere seen, I found 

 white earthy concretions rarely more than an inch or two in length, very irregular in 

 form, and usually more or less botryoidal. They seem to be a little more calcareous 

 than the surrounding mass. On breaking them open I could not detect any fossil 

 around which they might have segregated, as is sometimes the case in these bodies. 

 They are perfectly homogeneous in structure. East of the road the sharp peak of 

 Diego Campo rises, according to barometrical measurement made by Mr. Pennell, 

 3,855 feet above the sea, the highest point in the Monte Cristi range. That gentle- 

 man reports its summit to be of limestone. 



From Alta Mira to the little streams which form the head of the Isabella the road 

 runs along a very muddy clay ridge, where nothing can be seen of the geology ; but 

 further on, the shales with occasional sandstone beds are seen to have dipped north- 

 ward again, and only pebbles of these sandstones are found in the beds of the water- 

 courses. A little further along a coarse, soft, grayish-brown sandstone occurs, dipping 

 at a vei'y low angle northward, and full of the characteristic foraminifera, especially 

 Orhitoides, which have so often proved usefnl in identifying the formation. Still 

 further north on the summit of the last ridge the limestone occurs capping the ridge 

 as a brown or coarse-grained gray or even white rock, in almost every case full of 

 foraminifera. In one place it is of a pinkish white and without these fossils. 



On descending the north face of the ridge about four or five miles back of Puerto 

 Plata a marked change takes place in the rocks. The absence of good outcrops here 

 makes it difficult to be very certain about this part of the section. A series of 

 metamorphic sandstones, some of them micaceous, crop out on the road. They are 

 nearly horizontal, dipping slightly to the north. A more extensive study of the 

 suiTOundino- reg-ion leads us to believe that these are the base of the Tertiary, altered 

 by c(mtact with the Cretaceous, which has pushed them up and which cro])s out very 

 near here. Their dij) and even their lithological structure he!}) to corroborate this 

 theory ; and thus we have here a repetition ol' the state of affairs at Ta1)era. on the 



