MUSEUM OF COMPARATIVE ZOOLOGY. 261 



the jiresent 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 unmistakaMj 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 tliat, 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 tack 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 reumants 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 remnants of 

 older and higher levels which have been presrrved in this manner. In 

 fact, the erosion has been so great that tlie limestone is almost removed, 

 e.Kcept where preserved in ■':;olated mountain buttes like the Sierra Yun- 

 que and the Pan de Matanzas, and headwater ei'osion is constantly de- 

 stroying the remnants of the original limestone plain by deepening the 

 cols down to tlie metamorphic floor. Granting that the older limestones 

 once extended over most of the islaml in the contour of a low dome, 

 and that this arch has un ergone several periods of intermittent eleva- 

 tion with corresponding intervals of rest, accompanied by base levelling, 

 the topography can be more easilv 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 colnrnda, 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 varv in size from many square miles 

 to a few arrcs. Even the small {)Iaius, when entirely encircled by 



