1882.] 125 [Crosby. 



see distinctly that the adjacent sea-bottom is paved with growing 

 hemispheres of Astrea and Meandrina — the summit of a new 

 reef which will probably be elevated in its turn. 



This lowest platform varies in width from a few rods to a mile 

 or more. Sometimes the ground descends away from the shore, 

 indicating that the reef, during its formation, was a barrier-reef 

 at these points. Near the landward side of the reef, and espec- 

 ially toward the bottom, as may be observed in the natural sec- 

 tions, the coral-limestone is interstratified with layers of sand and 

 gravel, material washed from the hills while the reef was growing. 

 These beds are generally horizontal or slightly inclined toward 

 the sea. As we should naturally expect, this fragmental material 

 is most abundant near the mouths of the rivers, where the reef is 

 sometimes principally composed of it, showing that the modern 

 river-valleys are older than the reef. 



The second reef rises steeply, often perpendicularly, from the 

 inner edge of the first ; and, along the north coast, where most of 

 my observations were made, its altitude varies from 200 to 250 

 feet, the variation being due to unequal erosion. This reef, owing 

 to its longer exposure to the agents of denudation is much less 

 continuous than the first, and more frequently reposes directly 

 upon the ancient and non-calcareous mountains, though a well- 

 marked valley often intervenes, running parallel with the reef 

 and the coast. Being much older than the lower reef, the lime- 

 stone is distinctly more crystalline, and the corals and shells are 

 in great part obliterated, so that much of the rock appears quite 

 destitute of organic remains. But the points of resemblance 

 between the two reefs are sufficient to show that, in origin, they 

 are identical. 



The altitude of the third reef is about 500 feet. It differs from 

 the second very much as that differs from the first, having suffered 

 greater erosion and being still more solid and crystalline. And 

 the same is true concerning the relations of the third reef to the 

 fourth, which can be observed only at infrequent intervals along 

 the coast. In the neighborhood of the Yumuri River, 15 to 20 

 miles east of Baracoa, it is well preserved, with an elevation of 

 probably not less than eight hundred feet. 



These limestone terraces or ancient coral-reefs extend, with 

 slight interruptions, around the entire coast of Cuba. And in 



