Vol. 57.] PHYSICAL DEVELOPMENT 01* ST. KlTTS, ETd. 541 



of deep excavations into the borders of the highlands was subse- 

 quent to the formation of the marl-beds, which are supposed to 

 belong to the close of the Pliocene Period. Although the data for 

 studying these deep valleys are more fragmentary here than among 

 some of the neighbouring groups of islands, yet they are found to 

 have the same characteristics. The surfaces of the shelves between 

 Statia and St. Kitts, and again south of Nevis, have the undulating 

 features of erosion of elevated plains inside the margins bounding 

 their slopes, and indicate that the volcanic ridges, upon the St. Kitts 

 chain of islands, were largely built over an old erosion-surface and 

 plains like the Saba Banks. Furthermore, it appears that the 

 growth of the volcanic mountains is one of recent date, without 

 the igneous disturbances extending beyond the limits of the ridges 

 themselves. 



Subsequent to the production of the erosion-features just described 

 as characterizing the early Pleistocene Period, the next evidence 

 bearing on the geological history is seen in the ravines of small 

 size which dissect the gravels near Old Eoad, consequently a late 

 Pleistocene feature. The fringing-banks about the islands are 

 also somewhat channelled, to 60 or 75 feet below the surface, 

 showing that the land was at least that amount higher when 

 they were formed than now. By this elevation Nevis was con- 

 nected with St. Kitts for the last time, since when a considerable 

 time must have elapsed, sufficiently long for some changes in 

 the land-molluscs to have been effected. In this connection 

 Dr. Branch informs me that a larger species of Dentularia (a 

 subgenus of Helix)^ and Bulimus elongatus, Pff. (belonging to a 

 subgenus of Helix), are no longer living in St. Kitts, although abun- 

 dantly found there as sub-fossils, while the species, in a degenerate 

 form, survive in Nevis. The ravines, excavated out of the 

 gravel-formation and now refilled by a newer deposit to a depth of 

 40 or 50 feet, show the subsequent sinking of the land to this 

 amount, followed by a re-elevation. These changes of level have 

 their counterpart in the neighbouring islands. All other erosion- 

 features of the islands are only such as are in progress at the 

 present day. 



IX. Summary and Conclusions as to Changes of 

 Level of Land and Sea. 



The Saba Banks and the foundations of the adjacent islands rise 

 above the floor of the submarine Antillean plateau as tablelands, 

 with their margins indented by embayments, similar to the banks 

 of the St. Martin and Antigua groups, and so it is inferred that 

 the area underwent the same physical history : — namely, tablelands 

 rising to 2000 feet or more, during the earlier Miocene-Pliocene 

 Period ; followed by a partial sinking that prevented the complete 

 dissection of the region, and left the Saba Banks and the foundation- 

 plains of the volcanic islands (on one of which there is a fragment of 



