hill: geology of Jamaica. 31 



To the ordinary traveller this back coast topography is priucipally 

 interesting from its scenic features. To the topographer it reveals a 

 series of most interesting ancient terrace levels, which give important 

 testimony concerning the history of the island. Some of these are 

 beautifully shown on the east side of Montego Bay (see Plate XX.), 

 where six distinct levels or benches separated by deep slopes rise above 

 the sea in stair-like arrangement. At no other single locality are so 

 many of these levels shown in such close juxtaposition but one or more 

 of them can be individually distinguished at many localities entirely 

 around the island, as well as some others as high as 2,000 feet. At a 

 single glance these terraces in Jamaica do not present the perfection of 

 the allied phenomena exhibited on the southeast coast of Cuba, but 

 nevertheless, they record a similar geological history. 



Naturally the integrity of these levels varies with their relative age 

 and altitude. Those of higher altitudes are more fragmentary because 

 degradational processes have been working upon them longer. Frag- 

 ments of the lower benches are better preserved, although much broken 

 by erosion, while none of them are as perfect in contour as the benches 

 of the Coastal Plain. All have been cut across by rivers, etched and 

 dissolved by rainfall, and undermined by encroachment of the waves, so 

 that they are now often indistinct, but there are sufficient remnants in 

 Jamaica to enable the student of geomorphology to recognize them. 



Without an accurate topographic survey of the island, it is impossible 

 to correlate correctly all the different benches or to do more than approxi- 

 mate their altitudes. The following general statements concerning them 

 are based upon personal observations. The high sky line of the back 

 coast border, as seen from the sea, in some cases represents the survival 

 of the oldest summit topography of the plateau, and in others benches 

 and terraces which have been successively cut out of it during inter- 

 mittent periods of elevation. The highest of the old benches is John 

 Crow Ridge, a long narrow shoulder which is seen in approaching the 

 island from the Windward Passage ; it projects seaward from the Blue 

 Mountains and extends from back of Northeast Point near Port Antonio 

 southeast to Holland Bay. It may be a remnant of the summit topog- 

 raphy of the old plateau level. It is apparently a continuous hori- 

 zontal plateau composed of several patches of level surface, ending to 

 the southeast with the area known as the " Big Level." The interior 

 or landward side of the John Crow Plateau is now separated from the 

 Blue Mountain Ridge by the tremendous ravine of the Rio Grande. 

 The higher summit of Yallahs Mountain on the south coast (see Plate 



