102 GEOLOGICAL RECONNAISSANCE OF THE DOMINICAN REPUBLIC. 



either near the top of the Gurabo formation or the Mao Adentro limestone. 

 The collection from station 8783 (El Morro de Monte Cristi, altitude 153 

 meters) represents the Gurabo formation, and that from station 8774 (alti- 

 tude 155 meters) probably belongs to the same formation. These deter- 

 minations essentially corroborate the opinion of Doctor Maury regarding 

 the age of these beds. 1 The collections from stations 8777 and 8778 are 

 apparently from a horizon high in the Yaque group, for they include Area 

 (Scapharca) patricia Sowerby, which was collected by the Maury expedi- 

 tion 2 on Rio Cana from beds in the upper part of the Gurabo formation or 

 above the Gurabo formation. This species was not collected by the 

 expedition of 1919 on the south side of the valley of Rio Yaque del Norte. 



YAQUE GROUP, SOUTH SIDE. 



Although the fossils collected from the Yaque group on the south side of 

 the Republic are numerous and comprise more than 50 species of corals, 

 about 120 species of mollusks, and many other organisms, including abun- 

 dant unidentified Foraminifera, they afford no adequate basis for precise 

 correlation of the formations of the south side with those of the valley of 

 Rio Yaque del Norte. This is due to lack of precision in the data on the 

 stratigraphic relations of the beds from which the collections were made and 

 to apparent mixtures of faunas of different ages at some of the localities. 

 One locality that appears to be the correlative of the upper part of the 

 Gurabo formation is station 8622, where at least 9 out of 14 species of 

 corals seem to be common to the Gurabo. At station 8621, however, which 

 according to the field notes is stratigraphically higher than station 8622, 

 the Mollusca indicate that the horizon is that of the Cercado formation. 



The collections from stations 8572, 8590, and 8760 include a species of 

 Orthaulax that, according to Doctor Cooke, is [Orthaulax aguadillensis 

 Maury, which is found also in the upper Oligocene Cevicos limestone of the 

 Cibao Valley and in the Aguadilla limestone of Porto Rico. The collec- 

 tions from stations 8572 and 8590 probably represent more than one horizon. 

 The Mollusca collected at stations 8570 and 8760, apparently from a 

 single horizon, indicate that the south side Orthaulax horizon occupies a 

 position between the Baitoa formation and the Cercado formation or even 

 higher. Aside from Orthaulax this horizon is characterized by a new species 

 of Scapharca that closely resembles Area (Scapharca) patricia Sowerby. 

 In the valley of Rio Yaque del Norte A. patricia is apparently confined to a 

 horizon in the upper part of the Yaque group. 



Perhaps some beds at other localities may be correlated with some on the 

 north side after the collections have been more critically studied, but as the 

 collections can not be referred to their precise positions in the stratigraphic 



1 Maury, C. J., Bull. Am. Paleontology, vol. 5, p. 450, 1917. 

 'Idem, p. 441. 



