Yol. 57.] PHYSICAL DEYELOPMENT OF GUADELOUPE. 517 



when the Lower Petit-Bourg and Lafonde gravels were largely 

 removed by denudation. 



The evidence of this great elevation is shown in the compara- 

 tively narrow, but very deep valleys, dissecting the older rounded 

 topographic forms. Thus, between The Saints and Guadeloupe is 

 a narrow valley less than 2 miles in width, reaching to a depth 

 of 900 feet, or 700 feet deep in the submerged plain or bank. It 

 deepens to 1200 feet a few miles westward, beyond which it attains 

 a depth of 3000 feet. The data for determining the depth of the 

 channel, through the embayment of earlier origin, between Marie 

 Galante and Petite Terre, have not been obtained, though it is known 

 to be greater than 2000 feet. Between the south-eastern extremity 

 of Grande Terre and Desirade, where the plains are sunk to only 

 66 feet, there is an amphitheatre or cirque, with a depth of 990 

 feet, deepening to 1122 feet, and farther seaward to 1720 feet, 

 beyond which no soundings have been taken. The valley between 

 The Saints and Marie Galante is now drowned to 792 feet, and 

 the descent to the broad depression beyond is very rapid. 



The deep indentations of the sunken border of the western side of 

 Guadeloupe proper tell the same story of a former great elevation, 

 when the gorges were being channelled out by rapidly-flowing 

 streams. Thus, north of Basse Terre there is an indentation with a 

 depth of 810 feet within the limit of the coastal plain. Opposite 

 Ferry Point, a depth of 1740 feet is reached within the limits of the 

 submarine bank, w^here it is covered by only 246 feet of water. 

 At the north-eastern angle, there is another valley seen at 1980 

 feet. South of The Saints, and between them and Dominica, the 

 channel reaches to a depth of 3294 feet, indenting the submerged 

 ridge between the two islands. This is the height to which the 

 region was elevated so far as the evidence directly obtained from 

 Guadeloupe bears testimony, but a much greater altitude is 

 indicated beyond the immediate area. 



The epoch of great elevation and stupendous erosion, culminating 

 in deep valleys, was in the early Pleistocene Period, after the 

 introduction of recent types of life ; but from the evidence of the 

 deposits on the American continent, with similar geological 

 associations, it was during, or prior to, the early Glacial time. 

 It may be added, parenthetically, that to this epoch the abrupt 

 features of the escarpment east of Port Louis owe their origin, when 

 the streams on the tableland began to deepen their courses. 



Then followed a subsidence, during the accumulation of the 

 Upper Petit-Bourg Series, to a depth of 100 feet or perhaps some- 

 what more. The depressions now forming the isthmus became 

 covered with the mantle of the loams and gravels of this series — a 

 Mid-Pleistocene deposit. 



The succeeding rise of the land carried it above the present 

 height, when the rapid streams made channels across the plains, 

 now covered by the two very shallow bays north and south of the 

 isthmus', containing many islets, some of which are the remains of 



