ON THE GEOLOGY OF BARBADOS. 237 



'* One of the most striking features presented by the island of 

 Cuba, when viewed from the sea or from salient portions of the 

 coast, are the broad, level, and vertical-walled terraces or shelves of 

 rock which rest against the jagged mountains of the interior, and 

 form the shore around almost the entire island. I have observed 

 these terraces lying at various levels from twenty up to nearly two 

 thousand feet above the sea." 



The first terrace he describes as having a uniform altitude of 

 about 30 feet for hundreds of miles, unbroken save where rivers 

 have cut through it, and varying in width from a few rods to a 

 mile or more. The rock is largely made up of recent- looking corals, 

 but on the landward side natural sections show some inters tratified 

 layers of sand and gravel. 



" 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. . . Being much older than 

 the lower reef, the limestone 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." 



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

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

 greater erosion and being still more solid and crystalline." 



Remnants of a fourth reef occur at intervals, and its elevation 

 appears to be about 800 feet. " These ancient coral-reefs extend, 

 with slight interruptions, around the entire coast of Cuba." He 

 states that they are better preserved in the western than in the 

 eastern part of the island. 



Mr. Crosby then describes the mountain called El Yunque, situated 

 to the west of Baracoa, and rising to a height of 1800 feet. Up to 

 a height of 800 feet the mountain consists of ancient eruptive rocks 

 and slates, but from that height to the summit there is crystalline 

 limestone, which he considers to be part of a still older reef, and to 

 which he attributes a thickness of 1000 feet. 



If, however, the El Yunque limestone is really reef-rock, it is 

 probably in the form of a series of reefs covering and investing an 

 interior dome of older rock, and not in that of a solid mass 1000 feet 

 thick in the centre. When, therefore, Mr. Crosby argues that reefs 

 of such great thickness could not have been formed during elevation 

 because the corals could not grow in water 1000 feet deep, he is 

 basing an argument on an unproved assumption. He also states 

 that the third reef " includes not less than 400 feet in vertical 

 thickness of coral rock," but he omits to say how he formed the 

 estimate ; no measurement except that of a well or boring, or a 

 vertical cliff, would be free from doubt. 



Moreover, it is highly probable that the lower part of the reefs, 

 as in Barbados, consists of debris-rock, and does not contain coral- 

 masses in the position of growth. Prof. Alex. Agassiz has suggested 

 that much of the Cuban reef-limestone may be similar to the 

 Yucatan and Florida limestones, which consist of the shells and 



Q.J.G.S. >To. 186. K 



