GEOLOGY AND PALEONTOLOGY OF THE CANAL ZONE. 263 



All of the fossil reefs discussed in the foregoing remarks were 

 formed during periods of subsidence that followed subaerial erosion 

 of their basements. The basal contacts might be interpreted as 

 supporting Darwin's hypothesis, but in four of the six instances the 

 reefs are buried under later nearly pure limestones in which there are 

 few or no corals. What caused the change in the character of the 

 sediments, and coincidently led to the extermination of the reefs is 

 not known; but the organisms in the overlying sediments indicate 

 shallow, tropical waters, and as the geologic formations are areally 

 extensive (relatively speaking), they were evidently formed on 

 submarine flats. The corals began to grow on such flats and were 

 ultimately killed. So long as the ecologic conditions were favorable, 

 the corals flourished, but died when the conditions changed. The 

 formation of the flats can scarcely be attributed to the corals. 



WEST INDIAN MIOCENE REEF CORALS. 



Meager developments of reef corals during the Miocene occur in 

 Cuba and Santo Domingo, but at present no Miocene reefs are known 

 unless the name reef be applied to the corals found in the La Cruz 

 marl, eastward from La Cruz to the intersection of the railroad with 

 the highway from Santiago to the Morro. The La Cruz marl is a 

 bedded formation in which there are a few reef corals. The presence 

 of pebbles in the basal part of the formation at the south end of 

 Santiago Harbor suggests an erosion unconformity with some older 

 Tertiary formation. 



No Pliocene reef corals are at present known in the West Indies. 

 The erroneous suggestion, that a coralliferous limestone exposed in 

 a quarry on Calle Infanta, opposite Castillo de la Punta, Habana, 

 might be Pliocene, has been corrected on page 224. This limestone 

 seems to represent very nearly the same horizon in the Miocene 

 as the Bowden marl of Jamaica; it may be stratigraphically somewhat 

 higher. It contains some corals of reef facies but it can not appro- 

 priately be called coral-reef rock. The stratigraphic relations of the 

 base of the deposit are not known. 



"WEST INDIAN PLEISTOCENE REEFS. 



The West Indian Pleistocene reefs, whose stratigraphic relations 

 have been critically investigated and can be discussed here are those 

 of Jamaica and Cuba. Mr. R. T. Hill has placed in my hands a 

 manuscript describing the Pleistocene reefs of Barbados, and Doctor 

 MacDonald will discuss those of Costa Rica and Panama in his memoir 

 on the geology of the Canal Zone and adjacent areas. 



The basal contacts of the Jamaican Pleistocene reefs, as has been 

 elaborately presented by R. T. Hill in his account of the Jamaican l 



1 Hill, R. T., The geology and physical goography of Jamaica, Mus. Comp. Zool. Bull., vol. 34, pp. 90-99, 

 1899. 



37149— 19— Bull. 103 6 



