GEOLOGY AND PALEONTOLOGY OP THE CANAL ZONE. 261 



mation to which C. P. Berkey later applied the name Arecibo forma- 

 tion.^ I have no field acquaintance with the formation but from 

 some notes on it made by Cleve, before it had been named, from the 

 descriptions of Hill and Berkej,'', and from some of the corals collected 

 by members of the New York Academy Porto Rican investigations, 

 I am inclined to the opinion, that there is not a ''formation" but a 

 group of formations of similar lithology, for the "formation" contains 

 both middle Oligocene (Antiguan) and upper Oligocene (Anguillan) 

 fossils, and probably also some Miocene species. Ultimately the 

 "formation," as Berkey also has suggested, will probably be split 

 into several formations; it seems to mo that there will be at least 

 three and perhaps more. Only the stratigraphic relations of the base 

 of the formation particularly need consideration here. These rela- 

 tions are those of unconformity according to Berkey, who says:^ 



Above it [the Arecibo formation] in all cases lie the recent alluvial deposits and the 

 San Juan formation, and below it lie the older and more complicated igneous and 

 sedimentary rocks. The break between these two represents the chief unconformity 

 in the whole geological column. 



An excellent illustration of the unconformity below the ''Arecibo" 

 is given on page 16, figure 3, of Berkey's paper. 



Berkey says in his summary of the geologic history of the island:^ 



Where more simple marine conditions came into control, as would happen when 

 submergence or planation had masked or destroyed the more elevated soiu'ce of sup- 

 ply, the deposits became almost wholly reef limestones and shell limestones, with 

 only minor amounts of strictly detrital material irregularly distributed. 



The middle Oligocene reef-coral development of Porto Rico, there- 

 fore, took place after its basement had been subaeriaUy eroded and 

 then depressed below sea level, and it seems that the basement prior 

 to its submergence had been almost reduced to a peneplain surface. 



CUBA. 



Reef corals of middle Oligocene age were fu^t collected in Cuba, 

 on Rio Canapu, by Arthur C. Spencer, who obtained three species, 

 all of which also occur in Antigua; but the only at all extensive col- 

 lection is from the vicinity of Guantanamo, and was made by O. E. 

 Meinzer, who studied in detail the stratigraphic relations of the coral- 

 liferous formation. I am taking the following note from a manu- 

 script by Mr. Meinzer, now awaiting publication. That there is a 

 pronounced unconformity is indicated by a conglomerate at the base 

 of the formation. Previous to the submergence, during which the 

 coral reefs were formed, there was a long period of subaerial erosion, 

 but geologic investigations have not been prosecuted over large 



1 Berkey, C. P., Geological reconnaissance of Porto Rico, New York Acad. Sci. Ann., vol. 26, pp. 12-17, 

 1915. 



2 Idem. p. 3. 

 sidera. p. 59. 



