196 



ON THE TOrOCKAPllY AXD CEOLOCiV 



I have stated elsewhere that with a single exception all of the ernptive rocks of 

 Santo Domingo are granitoid, and usually well-defined syenites. That exception was 

 found in the Eani Iliver in the form of a few pebbles of an unmistakable porphyry. 

 It is apparently I'rom a small dyke, judging Irom the few pieces found. I was not 

 fortunate enough to detect it in place. It is a nearly l3lack matrix of fine grain, filled 

 with tabular ciystals of white feldspar an inch across. 



The plains about Bani have been referred to above as being covered with the 

 usual Post Pliocene formation in the shape of a deposit of coast gravel. Although 

 this extends uninterruptedly to the Avestward, the greater part in this region was 

 probably derived from the Ocoa River. At Honduras where the river first issues 

 from the hills, it is very coarse and contains great quantities of large boulders, some 

 of which are but partially rounded ; but further out on the plains, both south and 

 east there are fewer and smaller, and the preponderance of sand greater. Betw^een 

 the hills of the Pueblo and las Tablas the deposit forms a broad gravell}'' plain, covered 

 with grass and overgrown with thickets of acacia and cactus. Scattered over it are 

 a few lagoons, or rather small ponds which furnish a perennial supply of water for 

 animals. On the margin of two of these are collections of houses known respectively 

 as Caila Fistula and Matanzas, while near the foot of the hill of las Tablas is another 

 settlement of the same name. The latter is on a small stream running down from 

 Honduras. Three roads connect this region with that to the west. One crosses the 

 Ocoa River at Savana Buey and follows the coast to Azua. The second passes 

 through las Tablas and crosses a high hill called the ISTumero, uniting with the first 

 a few miles east of Azua, while the last runs southwest aci'oss the mountains from 

 Man i el. 



The coast road after crossing the broad shingly bed of the Ocoa and a few low 

 gravel hills, traverses some salt mashes adjoining the beach, and then follows the 

 coast around the east side of the" Bay of Ocoa. On passing some low hilly points it 

 shows slate cropping out on the beach with southern dips, but most of the way is 

 either on the sea beach or immediately inland on the di'ifted sea sand. 



Approaching Azua the Post Pliocene gravel is soon encountered, but there is 

 nothing to distinguish it from that noAV in process of deposition. In fact, there is 

 little doubt, but that its formation has gone on uninterruptedly ; and if it could be 

 examined, that of yesterday would be found continuous and conformable with the 

 most ancient portions inland. ' . : 



The I'pad over the I^umei'o runs around the north side of the Tablas hill, ci'osses 

 the river, and then mounts the slope of the hill. The rocks are coarse sandstones and 



