1897-98]- LATE FORMATIONS AND GREAT CHANGES OF LEVEL IN JAMAICA. 



345 



Bay, which may be partly illustrated in Map, Figure 6. At the ends of 

 the district shown on the Map, the White Limestones have been 



FiGL'RE 6. — Map from Port Antonio westward; showing^ the erosion of gorges through the mountain 

 plateau, (" White Limestone," shaded portion), 700-1,000 feet above tide. 



removed for distances of three or four miles, with the formation of com- 

 pound valleys in the older strata. Along the rivers, shown on the Map, 

 (Figure 6), there are the remains of upper broad valleys deepened into 

 narrow canjoHs along the streams, the relative sections of which are shown 

 in Figure 7. 



Figure 7.— Section of natural proportions taken from a photograph of the outlet of Swift River (near 

 Hope Bay). Higher part of mountain about 1,000 feet ; canyon (cj (concealed by its windings from the 

 exterior view), whose bed is only from 50 to 150 feet wide ; / p, the section of the valley formed during its post- 

 Layton or early Pleistocene base level ; and / /, that formed during the Liguanea base-level. 



The secondary valleys are not broad undulating plains and ridges, 

 such as characterized the Mio-Pliocene erosion, but such as result from 

 the widening of old gorges by rains and streams as shown in Figure 7. 

 Behind the coastal highlands of White Limestones (as in Figure 6), 

 there are large valleys bearing a relationship to the depressions across 

 the rocky highlands (such as 1. 1. in Figure 7). These are surrounded 

 by amphitheatres of hills, all showing gradients which in part reach to 

 .several hundred feet per mile — in .short, like gigantic washouts. While 

 the canyons record the amount of recent elevation, yet the valleys above 

 them indicate that the higher work of the streams dated back to the 

 great post-Layton or Pleistocene elevation. 



