284 Miscellaneous. 
In the precipitous mountain called El Yunque (the Anvil), five 
miles west of Baracoa, reef-limestone, 1000 feet thick, constitutes 
the upper half of the mountain, the lower part, on which the reef 
rests, consisting of eruptive rocks and slates; and originally the 
upper limit of this modern limestone formation must have been 
2000 feet above the sea-level. Mr. Sawkins gives 2000 feet as 
the maximum thickness of the Jamaica elevated coral reefs above 
the sea. 
Evidence that the reefs were not formed during a progressive 
rising of the land is drawn from the thickness of the reefs. Mr. 
Crosby observes that the reefs reaching to a height of 500 and 
1000 feet, if not also to that of 2000 feet, show, by the remains 
within them, that they were made chiefly of reef-building corals, 
and hence that they were not begun in deep water, as is assumed 
in the theory of Mr. Agassiz, but that they were made in shallow 
water during a progressive subsidence. Mr. Crosby concludes as 
follows :— 
“We have then apparently no course but to accept Darwin’s 
theory as an adequate explanation of the elevated reefs of the 
Greater Antilles, and therefore to admit that the upheaval of this 
portion of the earth’s crust has been interrupted by periods of 
profound subsidence during which the reefs were formed. The 
subsidence of 2000 feet, of which El Yunque is a monument, 
must have reduced the Greater Antilles to a few lines of small 
but high and rugged islands; but, as Mr. Bland has shown, this 
fully accounts for the absence in these immense tracts of all large 
animals, although they were abundant here in Phocene and earlier 
times.” : 
The writer adds here the following objections to the theory of 
the formation of coral atolls in deep waters out of the calcareous 
secretions of deep-water life :—(1) It is very improbable that sub- 
marine eruptions ever make the large and well-defined craters, 
like those of subaerial action, which are appealed to in order to 
explain the lagoon feature of atolls; (2) Many coral atolls are 
twenty miles or more in diameter, which is vastly larger than 
the largest of craters; (3) The atolls are never circular, and the 
larger have the irregularities of outline or diversities of form cha- 
racterizing other large islands of the ocean ; (4) In the actual reefs 
and islands of the Feejee group (see the map of the islands in the 
writer’s ‘Corals and Coral Islands’) all the conditions, from the 
first stage to that of the almost completed atoll, are well illustrated, 
one island having only a single peak of rock within the lagoon, not 
thy of the whole area, which a little more of subsidence would put 
beneath the waters and leave the lagoon wholly free.—J. D. Dana, 
in Silliman’s American Journal for August 1883. 
