128 J. W. SPENCER — RECONSTRUCTION OF ANTILLEAN CONTINENT. 



ending later in one region than in another, but the general undulations 

 belonged to the same system of changes of level. 



The Earlier Pleistocene Antillean Continent and its Degradation. 



After the deposition of the Matanzas limestones and the Lafayette 

 loams, the continent rose to a great elevation, as is recorded in the 

 amount of succeeding erosion. The enormous degradation is one of the 

 physical problems which McGee so strongly emphasizes in his researches 

 in the Lafayette.* He considers it greater than that of the Pliocene 

 elevation. For the Antillean region, the writer is not fully satisfied with 

 his conclusion in this first study, although the filling of many of the 

 old Pliocene valleys was almost entirely removed, and in many yilaces 

 the channels were further enlarged. At present, the writer thinks that 

 the degradation in the pre-Matanzas and in the post-Matanzas epochs 

 was of about the same magnitude, but a longer duration of erosion in the 

 earlier Pliocene period would explain the inferior elevation of that time. 

 In both periods the valleys were excavated so as to leave depressions 

 several miles in width, not merely along the great rivers of the continent, 

 but also along the shorter streams of the West Indies. Thus the Yumuri 

 valle}^ in Cuba was reexcavated to a width of three miles, and Xagua 

 bay to a greater breadth, for this is only a recently submerged valley. 

 The same is illustrated on the south side of Jamaica (in Vere and West- 

 moreland parishes) and in Haiti. In Costa Rica the effects of this epoch 

 of erosion are seen in the rounded hills rising out of the low plains and 

 in the broad valleys on the western side of the continent. Everywhere 

 the amount of denudation would indicate slopes corresponding to those 

 of the earlier Pliocene elevation. The fjord of Matansas bay, which has 

 a depth of 1,500 feet within its land boundary, is cut through this latest 

 Pliocene limestone. 



While the Pliocene valleys were more or less refilled in the Matanzas 

 epoch, it is certain that they were reopened in the earlier part of the 

 Pleistocene period. It would appear that the present lands of the West 

 Indies and the adjacent parts of the continent stood quite as high, if 

 not higher, than during the Pliocene elevation, so the amount of erosion 

 equaled or exceeded that preceding the Matanzas epoch. At any rate, 

 the fjords are open to the great depths already described. 



The character of the drowned valleys, involving the Matanzas lime- 

 stones and the Lafayette loams, and their physical relations to the succeed- 

 ing deposits, point to, the conclusion that the American continents were 

 united by the Antillean bridge with an altitude as great as that of the 



* Cited before. 



