96 GEOLOGICAL RECONNAISSANCE OF THE DOMINICAN REPUBLIC. 



The upper Oligocene deposits consist of the Cevicos limestone, which is 

 found in the Cibao Valley, and limestone on Monte Calavosa and near 

 San Cristobal, on the south side. The faunas are meager and the correla- 

 tion is uncertain, but if it is correct deposits of the same age occur in the 

 islands of Anguilla, Porto Rico (according to Maury), and Cuba, and in 

 Florida, Panama, and Trinidad. These deposits are tentatively correlated 

 with the Chattian-Aquitanian of southern Europe. Doctor Cooke (see 

 p. 63) has noted the uncertainty as to whether these deposits should be 

 classified as uppermost Oligocene or basal Miocene. 



MIOCENE. 



YAQUE GROUP, NORTH SIDE. 



Baitoa Formation. 



Only the corals and mollusks and one bryozoan of the Baitoa formation 

 have been identified. One species of coral, Goniopora sp., appears to be the 

 same as that found in the Chipola marl of Florida. The bryozoan Cupularia 

 denticulata Defr. ranges stratigraphically from the Chipola marl to Recent 

 in America. The most abundant fossils are Mollusca. The most conspic- 

 uous faunal break in the Tertiary system of the Dominican Republic indi- 

 cated by the Mollusca is that between the upper Oligocene and the Baitoa 

 formation. The fauna of the Baitoa formation closely resembles the suc- 

 ceeding Miocene faunas. Only two of the Baitoa superspecific groups, 

 the genera Orthaulax and Cymia, are not known in the later Miocene faunas 

 of the valley of Rio Yaque del Norte. The curious stromboid genus 

 Orthaulax, which is represented by the genotype 0. inornatus Gabb, has 

 been considered a typical Oligocene genus; but the faunal assemblage of 

 the Baitoa formation clearly indicates its Miocene (Burdigalian) age. 

 Phos semicostatus Gabb is the most characteristic mollusk of the formation. 

 The horizon of the Baitoa formation, which has not been found elsewhere in 

 the West Indies, is correlated with that of the Chipola marl of Florida. 



Cooke l has recently discussed the stratigraphic significance of Orthaulax. 

 In the Djminican Republic this genus, according to present information, 

 appears to range from upper Oligocene to middle Miocene. In contending 

 that the Quebradillas limestone of Porto Rico is upper Oligocene because 

 it contains Orthaulax in abundance, Hubbard 2 is expressing an opinion 

 once held, but unwarranted, that this genus is restricted to the Oligocene. 

 Doctor Maury 3 has, however, referred the Quebradillas limestone to the 

 lower Miocene. 



Cercado Formation. 



The faunal lists for the Cercado formation embrace all fossils collected 

 in 1919 except the Foraminifera, which have not yet been studied, but lists 

 of Foraminifera obtained by Doctor Maury are included. This formation 



' Cooke, C. W., Abstract, Geol. Soc. America Bull., vol. 31, p. 206, 1920. 

 2 Hubbard, Bela., Science, new ser., vol. 51, p. 396, 1920. 

 •Maury, C. J., Am. Jour. Sci., vol. 48, p. 212, 1919. 



