MUSEUM OF COMPARATIVE ZOOLOGY. 261 
the present rate of denudation, it must have been a large amount, for in 
places it has laid bare the old metamorphic floor. Wherever I have seen 
the latter, it unmistakably shows that it was once covered by the lime- 
stone. This is well shown in the accompanying section across the island, 
through Havana, where the older foundation rocks always appear in the 
valleys of erosion beneath the escarpments of stratification formed by 
the adjacent limestones, the latter being so tilted around their periphery 
that, clearly, they once extended over them, as at Villa Clara. It is 
easy to conceive that, if erosion proceeds in the future as in the past, 
without further elevation of fringing coast deposits, the island will ulti- 
mately be planed down to its original core of serpentine and allied rocks, 
without material alteration of its coastal outline. 
The most ancient part of the longitudinal limestone arch, as back of 
Havana, has been removed down to the older metamorphic rocks, and 
a strip of the older limestone formations running parallel to the coast 
remains between this valley and the sea. (See Plate I. Figs. 1 and 2.) 
This, in turn, by a cross erosion of the streams, is serrated into frag- 
mental remnants of the limestone, like the Moro and Castillo Principe 
Plateaus at Havana. The Pan de Matanzas, near Matanzas, and the 
peculiar mountains of Moa and Yunque, near Baracoa, are remuants of 
older and higher levels which have been preserved in this manner. In 
fact, the erosion has been so great that the limestone is almost removed, 
except where preserved in isolated mountain buttes like the Sierra Yun- 
que and the Pan de Matanzas, and headwater erosion is constantly de- 
stroying the remnants of the original limestone plain by deepening the 
cols down to the metamorphic floor. Granting that the older limestones 
once extended over most of ‘the island in the contour of a low dome, 
and that this arch has undergone several periods of intermittent eleva- 
tion with corresponding intervals of rest, accompanied by base levelling, 
the topography can be more easily explained. 
Where the limestone is the prevalent formation, as in the sugar 
country of central Cuba, the surface is marked by extensive level tracts, 
covered with the deep residual tierra colorada, one of which plains is 
well shown in the accompanying photograph. (Plate VI.) The continu- 
ity of these plains is broken by abrupt hills, either single or in groups, 
some of which seem to have no persistent axis of direction, and are clearly 
remnants of the higher level below which the land has been degraded. 
The plains show very little slope to the eye, and project abruptly to the 
foot of these limestone hills. They vary in size from many square miles 
to a few acres. Even the small plains, when entirely encircled by 
