52 GEOLOGICAL RECONNAISSANCE OF THE DOMINICAN REPUBLIC. 



Central are probably much younger than the schists and serpentines of 

 the basal complex, which are exposed a few kilometers farther south, on 

 the road from Cotuf to Maim6n. 



Most of the hills in the vicinity of Maimon are composed of serpentine 

 that appears to be an alteration product of some basic igneous rock. On 

 Loma Pegado, about 4 kilometers southwest of Maimon, the serpentine has 

 weathered at the surface to a brick-red, highly ferruginous soil similar to 

 the lateritic iron ores of Cuba but too thin, where seen, to be of commercial 

 value. Near the top of Loma Pegado the serpentine is cut by a dike of 

 hornblende diabase. Near the foot of a low mountain southeast of Hatillo 

 there are exposures of granitic gneiss, but the mountain is composed chiefly 

 of chloritic schist, which near the summit of the mountain is impregnated 

 with copper ore. Near Hatillo the clay soil contains small boulders of 

 magnetite. A more detailed description of the iron and copper prospects 

 of this region is given on pages 228-231. 



The Constanza trail crosses slates, schists, tuffs, diorites, and serpentines, 

 which are cut by several kinds of dike rocks. The mountain at Las Minas, 

 northwest of Jarabacoa, consists of schist. El Barrero, south of Jaraba- 

 coa, is composed of serpentine. At Constanza there is greenish basalt tuff 

 cut by dikes of a fine-grained lamprophyre. Rio Limon and Rio del 

 Medio, southwest of Constanza, cut through fine-grained red and green 

 rocks and serpentine. 



A fault block of muscovite-chloritic schist, chloritic schist, calcareous 

 argillite, and diorite-gneiss north of San Jose de las Matas is separated from 

 the main body of the basal complex, which is bounded south of the town by 

 conglomerates and limestones, probably all of Oligocene age. At Bulla, 

 Rio Mao emerges from a gorge cut in laminated chloritic schist, which is 

 overlain unconformably by Miocene gravels. Outcrops of schist similar 

 to that near San Jose" de las Matas were seen also along the headwaters of 

 Rio Gurabo near the point where it is crossed by the trail from Moncion to 

 Sabaneta. Near the edge of the basal complex south of Sabaneta there are 

 exposures of blue sericite schist or phyllite, more or less gneissoid quartz 

 diorite, and hornblende schist. Associated with the schists, but probably 

 much younger, are lavas, tuffs, and porphyritic intrusions. Most of the 

 trail from Sabaneta to Restauracion passes over quartz diorite, which is 

 apparently intruded into schist and quartz diorite gneiss. Over the first 

 4 or 5 kilometers east of Restauracion green volcanic agglomerate and tuff 

 apparently rest with depositional contact upon the quartz diorite. 



Between Restauracion and Joca the geology differs considerably from 

 that farther east. Black basaltic rock, weathering to a serpentine-green 

 in places, local beds of coarse agglomerate, and a few siliceous dikes are 

 exposed over the first 8 or 10 kilometers from Restauracion. Beyond this 

 is hard purplish limestone, much jointed and veined and dipping steeply 



