164 bulletin: museum of comparative zoology. 



of which may be termed the Montpelier, the Bowden, the Manchioneal, 

 and the Pleistocene subsidences, and the succeeding elevations the Mid- 

 Oligocene, the late Miocene, and the early Pleistocene, or recent eleva- 

 tions respectively. It is interesting to note that these movements are 

 each successively smaller in amplitude than the preceding, like the dying 

 strokes of the pendulum. 



The erogenic or mountain folding movements were especially charac- 

 teristic of the earlier of the middle periods of its history, while the 

 epeirogenic events mark the later stages. The Post-Eicnmond, Post- 

 Moneague, and Post-Bowden uplifts were all of an erogenic character, 

 but each successively consisting of broader arching and less closely 

 folded deformation. Thus it is that the Richmond beds are closely 

 folded and overthrown, the Cambridge, Montpelier, and Moneague beds 

 arched and gently wrinkled, the Bowden beds only tilted. Collectively, 

 they probably represent the initiation, culmination, and expiration of 

 the great Antillean mountain uplifts. The elevated reefs recording 

 the epeirogenic movements were horizontally elevated without visible 

 deformation. 



An interesting fact of the structure of Jamaica, as well as the Antilles 

 in general, are the two lines of erogenic dominant trends, one extending 

 northwest and southeast, and the other east and west. Whether these 

 trends can be each associated with a peculiar effort of mountain making 

 we cannot form definite conclusions at present. It is very probable, 

 however, that all of the structure was originally dependent upon an an- 

 cient early Mesozoic orographic uplift or buttress, which had an east and 

 west axis through the Great Antilles and the Guatemala-Chiapas region, 

 the only trace of which is now preserved in the old Post-Paleozoic moun- 

 tains of the latter region and possibly Western Cuba. It is certain, 

 however, that the earliest movements visible in the present structure of 

 Jamaica had a northwest and southeast trend conformable to the direc- 

 tion of the present Blue Mountain ridge, and conformable to similar 

 trends in the combined coast line of nortlieast Cuba and Haiti and the 

 outer margin of the Baliama Banks. The later movements have east 

 and west trends (which might be called Antillean), as shown in the 

 secondary axis of the elevated limestone ridges of Jamaica, Cuba, Porto 

 Ptico, and the structure of the base of the Yucatan peninsula, the moun- 

 tains of Eastern Honduras, the Isthmus of Panama, and the Venezuelan 

 coast. It may be well to note here that it is impossible at present to fit 

 into either of these systems of trends — the Bahaman or Antillean — 

 all the Windward Islands or their submarine platforms. 



