GEOLOGY AND GEOLOGIC HISTORY. 61 



tion is variable but is prevailingly northwest. The dip is high, and in most 

 places, except where the beds are overturned, it is toward the northeast. 

 The age of this formation has not been ascertained, but it is manifestly 

 older than the Miocene deposits that adjoin it in fault contact on the south 

 and is probably either Eocene or Oligocene. No fossils were found in it. 



OLIGOCENE SERIES. 

 Tabera Formation. 



The name Tabera formation is here proposed for the strata exposed along 

 Rio Yaque del Norte in the vicinity of Tabera, a village on the east bank 

 of the Yaque about 20 kilometers south of Santiago. The formation con- 

 sists of alternate beds of blue-gray shale, sandstone, massive conglomerate, 

 and some beds of limestone. It rests with depositional contact upon diorite 

 or epidiorite and is overlain with marked angular unconformity by yellow 

 shell-bearing conglomerate and sand of the Baitoa formation (Miocene). 



The thickness of the Tabera formation can not now be stated with pre- 

 cision. Probably not less than 300 meters of strata are exposed at Baitoa, 

 and the lower beds, which outcrop farther upstream, are reported by Mr. 

 Condit to be considerably thicker. In the vicinity of Tabera Mr. Condit 

 noted more than 800 meters of shales and conglomerates referable to the 

 Tabera formation, and all these beds lie stratigraphically below the part of 

 the formation exposed at Baitoa. Unless some of the strata exposed are 

 duplicated by faulting, the Tabera formation is probably not less than 1,500 

 meters thick. 



The basal beds of the Tabera formation exposed along Rio Yaque near 

 the mouth of Arroyo Milac about 3 kilometers above Tabera consist of 

 about 10 meters of limestone, which grades downward from massive lime- 

 stone into conglomerate containing a few small, well-rounded pebbles of 

 igneous rock but consisting chiefly of angular or rudely rounded cobbles 

 of the dioritic rock upon which it rests. Large specimens of Lepidocyclina 

 are scattered through the calcareous part of the rock but the largest and 

 the most abundant are in the massive beds of limestone. The basal lime- 

 stone and conglomerate are overlain by a series of thick, dark-green sand- 

 stones and shales containing local beds of conglomerate. This series is 

 considerably sheared and crumpled and is cut by minor faults. About 

 600 meters above Tabera, on the Yaque, a 6-meter bed of conglomerate 

 apparently grades laterally (southeastward) into limestone containing the 

 Foraminifera listed on page 107 (station 8671). 



A double-peaked hogback about 1 kilometer southeast of Baitoa is com- 

 posed of limestone containing Lepidocyclina and corals (station 8672), 

 which appears to be of the same age as the conglomerate on Rio Yaque. 



The fossils collected from the conglomerate and sandstones of the Tabera 

 formation on Rio Yaque at and below Baitoa are listed on pages 107-108 

 (stations 8557 and 8673). 



