MUSEUM OF COMPARATIVE ZOOLOGY. 255 
irregularities having been levelled by solution. The formation averages 
about thirty feet in thickness, and usually extends inland only a short 
distance, often only a few yards, as on the northwest end of Moro Point, 
or not over an eighth of a mile, as at Baracoa, and is especially well 
exposed along the narrow points of the numerous small harbors, as shown 
on Plate LI. 
The soboruco is a topographic as well as a stratigraphic feature, for its 
surface is a bench gently sloping to the sea ; it has neither been covered 
by later deposits nor greatly denuded. It usually forms a cliff at the 
surf line, about fifteen feet in height, against which the surf beats with 
great force, wearing deep indentations. The spray breaks over the 
summit, with the aid of the sun producing the surface induration which 
is visible wherever rain or other moisture falls upon the hot limestones, 
or wearing the surface into cavernous Karrenfelder. This solution and 
induration at Baracoa, for instance, has converted the limestones in 
spots into a coarse saccharoidal marble, and has aided in the segregation 
of small lumps of iron ore direct from the coral. 
Where I was able to examine the base of the elevated reef rock, 
mostly at the mouths of rivers, it seems to have been deposited rather 
abruptly upon a semi-argillaceous terrane of silt, and occasionally very 
fine pebbles, which have been brought down and deposited by the rivers. 
(Plate II.) I did not find it growing upon the larger gravel which is 
deposited immediately at the river’s mouth, as is seen off the Yumuri of 
Baracoa, where the river empties into the sea, and not intoa bay. Further- 
more, the present submerged fringing reefs do not grow immediately 
where the rivers send their fresh waters into the sea, but are interrupted 
there by a barren area simulating a submarine channel, as is shown in 
the accompanying illustrations of the harbors. This fact has an im por- 
tant bearing upon the origin of the present circular harbors, and upon 
the theories of alleged subsidence, both of which subjects are more fully 
discussed in later pages. 
Is is impossible to describe all the localities at which the soboruco was 
observed.1 Sometimes, as along the Havana coast, it occupies a narrow 
coastal strip extending from the point of one harbor to another. Again, 
as on Moro peninsula, opposite Havana, it occurs only as a small patch 
in a slight indentation in the old headland composed of folded Miocene 
rocks. (Plate I. Fig. 2.) 
At Tanamo and other places on the north coast the soboruco not only 
1 See A. Agassiz, Bull. Mus. Comp. Zoodl., Vol. XX VI. No. 1, Plates XLIV.- 
XLVII. 
