Crosby.] 128 [ November 1, 



downward, yet the character of the sediments deposited during 

 that time shows that the movement was frequently reversed, 

 periods of elevation alternating with periods of subsidence, the 

 latter, however, predominating. Similarly in the case of Cuba, 

 during post-Tertiary time this region has experienced a powerful 

 elevation ; but there are good reasons for believing that the up- 

 ward progress of the land was not uninterupted. The reefs, in 

 fact, are witnesses for both sides, testifying with nearly equal 

 distinctness to both elevation and subsidence. 



The coast of Cuba is probably not rising iioav, at least not at 

 all points. On the beach near Baracoa the erect stumps of large 

 trees may be seen, standing where they grew, near the low tide 

 mark. 



The numerous harbors of Cuba are nearly all formed on one 

 plan, of which Baracoa harbor is a good example. It is an approx- 

 imately circular and almost completely land-locked basin, commu- 

 nicating with the sea through a narrow but deep passage between 

 broken walls of coral rock. The larger harbors dej>art from this 

 plan chiefly in their more irregular outlines, all agreeing in having 

 deep narrow mouths. Every harbor is at the mouth of one or 

 more rivers ; and their narrow inlets, as I conceive, are the work, 

 not of the sea, but of the rivers at a time when the land was 

 higher than now. While the main body of the harbor, in each 

 case, is simply the broader and older ])ortion of the river valley 

 behind the barrier-reef which has been invaded by the rising sea. 

 The circular form of many of the smaller harbors is largely due to 

 the fact that the sand brought down by the rivers is thrown up 

 by the sea into curved bars, cutting off the inequalities of the 

 shore. 



During the formation of the most recent of the elevated reefs, 

 which, as already stated, forms a level floor about thirty feet 

 above the sea, the mouths of the smaller streams were behind 

 the reef, discharging into irregular channels or basins between 

 the reef and the shore. On account of the turbidity and fresh- 

 ness of the water, the reef, especially on its inner border, grew 

 less rapidly at these points than elsewhere, the basins behind the 

 reef becoming filled with debris from the land. When the reef 

 was finally raised to something above its present level, each river 



