516 PEOF. J. W. SPENCEE ON THE GEOLOGICAL AND [NoV. I9OI, 



and south of the isthmus. This is also seen in the great banks 

 reaching to Petite Terre and Desirade, and about The Saints and 

 Marie Galante. The high bluffs of 100 or 150 feet along the eastern 

 coast and other points are the results of the recent encroachments 

 of the sea ; but the interior escarpment in the northern part of the 

 island is a somewhat older feature. Undulating outlines are 

 characteristic of the denudation of a country near the base-level of 

 erosion, lasting throughout a long period. The duration of land- 

 surfaces in Guadeloupe continued from the time of the early Miocene 

 emergence until that of the introduction of recent types of life, or 

 throughout the Miocene-Pliocene Period. The condition of low 

 elevation of the country mentioned, which obtained during the latter 

 part of the period, does not appear to have prevailed during the 

 whole time ; for we find the sunken plateau connecting the islands 

 having the form of broad depressions or undulating plains like 

 those of base-levels of erosion, though now 2000 feet below sea- 

 level. The drowned plains and ridges are modified by the deep 

 channels, some of which continue upward and extend to the deep 

 indentations of the island-plateau formed by streams descending 

 torrentially from ta.blelands. 



The recurrence of the Tertiary Limestones, etc., on several of the 

 adjacent islands suggests their late continuity. That the archipelago 

 of Guadeloupe was not bodily thrust up above the submerged 

 ridge by volcanic forces is shown in the physical difference between 

 the main island and Grande Terre, where the latter, as has been 

 seen, was not deformed, while the volcanic forces have only lifted the 

 high mountain-ridges where there has been late activity, and have 

 not differentially raised the islands in other districts which are 

 characterized by old eruptive basements. Upon this hypothesis, 

 the earlier Miocene-Pliocene elevation of Guadeloupe, during the 

 formation of the broad depressions between the islands, reached 

 an altitude of at least 2000 feet above that of the present day 

 (except the volcanic mountains of more recent date). Then the 

 Guadeloupe archipelago stood out as a plateau, like much of recent 

 Jamaica, with its escarpments and surfaces broken by atmospheric 

 denudation. 



The greatest of the broad valleys indenting the mass is that 

 between Marie Galante and Grande Terre. With the gradual 

 subsidence of the plateau, the encroachments of the sea modified the 

 now submarine escarpments, and eventually brought the tableland 

 so low that the recent features of Grande Terre could be produced; 

 but this comparatively low altitude must have been of long duration 

 to have allowed of the moulding of the rounded topography. 



Then followed the submergence to a depth of 200 feet below the 

 present height, with the accumulation of the Lafonde and Lower 

 Petit-Bourg Series, which was a comparatively short interval. This 

 episode was about the close of the Pliocene Period ; after which 

 there was another epoch of very great elevation and rapid denudation, 

 since the introduction of the recent fauna of the Usine Limestones, 



