THE WEST INDIAN BRIDGE. 



These sections, Fit's. 5 and 6. illustrate gradation plains and steps between the col of the 

 straits of Florida and the floors of the Mexican and Atlantic basins The cunonlike character 

 is shown bv the dissection of the continental shelf, whose floor is seen in broken shading. 

 The gradient of the Colorado Canon is also shown in Fig. 5. The depth of submergence is 

 given in feet ; and the mean slopes in feet for distances of a given number of miles. 



were not depressed by the terrestrial movements wliicli elevated 

 mountain zones or depressed ocean basins. A few of tbe submarine 

 valleys are parallel to the mountain ridges, and may have been 



