Reports and Proceedings — Geological Socielg of London. 283 



masses, from which it was disconnected by denudation during a very 

 long period of atmospheric activity, followed by a subsidence, so as 

 to bring the present surface of the submarine banks to a level so 

 low that the undulating features of a base-level of erosion could be 

 formed on them ; for, during the period when the deep and broad 

 depressions on the Antillean chain were being fashioned, the now 

 isolated island-groups stood out as table-mountains, which were 

 slowly being eaten away by atmospheric agents. There was next a 

 subsidence to about 200 feet below the present level, about the close 

 of the Pliocene period, followed by a re-elevation to 3,000 feet, as 

 shown within the area, but in reality much more. It was during 

 this early epoch of the Pleistocene that the great rodents described 

 by Professor Cope reached here from South America, but the race 

 continued to live here sufficiently long to give rise to distinct species. 

 The submergence of the mid-Pleistocene period was to the extent 

 of about 200 feet, and the subsequent elevation was marked by 

 moderate denudation with the production of shallow watercourses, 

 traceable across the sunken banks to depths of 150 or 180 feet. 

 Again there was a moderate depression sufficient to bring the 

 surface a few feet below the present level, succeeded by a rise during 

 which the low shell-bearing sands were formed. 



5. " On the Geological and Physical Development of the 

 St. Christopher Chain and Saba Banks." By Professor J. W. 

 Spencer, Ph.D., M.A., F.G.S. 



The St. Christopher (St. Kitt's) ridge rises from 2,000 to 2,800 feet 

 above the submarine Antillean plateau, and is for the most part 

 covered with shallow water, except between St. Kitt's and Mont- 

 serrat, where a depression I'eaches 2,592 feet, and between Statia 

 (St. Eustacius) and Saba, where it reaches 1,200 feet. Eelics of 

 old igneous formations are found on the islands, but in most places 

 they are covered by more recent volcanic formations. 



The Brimstone Hill Limestone is the succeeding formation, which 

 appears to be newer Pliocene or Pleistocene, and to correspond with 

 the Upper Marls of Anguilla and those at the Usine of Pointe 

 a Pitre in Guadeloupe. 



The St. Kitt's Gravels succeed, and in beds of apparently the 

 same age shells of living species have been found at an altitude of 

 300 feet. The main volcanic activity belonged to the mid-Pleistocene 

 period. It is inferred that the group underwent the same physical 

 history as the neighbouring groups of islands. First there was 

 elevation, followed by subsidence. Then came the second great 

 elevation to about 3,000 feet and erosion of the region, when the 

 deep valleys and cirques indented the margins of the tablelands, and 

 at the same time the great volcanic ridges were built. Next followed 

 another subsidence to about 300 feet below the present level, and 

 during this epoch the volcanic domes of Brimstone Hill and the 

 * Quill ' of Statia were formed. The succeeding upward movement 

 carried the land 60 feet or more above the present level, when 

 ravines and small channels in the sunken shelf were excavated. 



