1897-89- 



HIGH PLATEAU AND SUBMARINE ANTILLEAN VALLEYS. 



365 



Figure 4. — Sections of the submerged Cazonan valley (south 

 of Cuba). It is much shorter than the other sections shown, ;ind 

 somewhat resembles a great ampitheatre. 



Figure 5.— Section showing the descent of the valley descend- 

 ing from the Mexican plateau and emerging on the coastal 

 plains at Atoyac. 



FiGURK 6. — Section of a Mexican valley descending to Mon- 

 terey. 



These sections of valleys descending from the Mexican pla- 

 teaus are drawn on same scale as those submerged. The sec- 

 tions of submerged and l.md valleys arc here brought together 

 for purposes of comparison. 



The long reaches of the 

 Floridian Channel resem- 

 ble base levels, and may 

 be seen to have much more 

 gentle slopes than those of 

 the Colorado canyon (shown 

 on Figure 2). Indeed, 

 some of the drowned 

 stretches have gradients as 

 low as, or even lower than 

 those of the buried chan- 

 nel of the Mississippi. 

 Thus along portion of fig- 

 ure 2, for a distance of 1 1 5 

 miles, the gradient is only 

 one foot per mile ; and 

 along another part, for 65 

 miles, the declivity is re- 

 duced to six-tenths of a 

 foot. Even on the abrupt 

 slopes between the nearly 

 level reaches, for exam|ile 

 a distance of 65 miles, 

 the descent averages only 

 43 feet per mile ; and if 

 the Mexican valleys can 

 be taken as guides in in- 

 terpreting the submarine 

 features, it is probable that 

 more detailed soundings 

 would show the descent of 

 the floor to be made up of 

 almost level reaches sep- 

 arated by steps more pre- 

 cipitous than those shown. 

 Comparing this drowned 

 valley with the valley 

 above Atoyac, it may be 

 observed that for stretches 

 of eight or ten miles, the 

 mean dfescent of all the 



