324 Geological Society. 



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 3000 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 Prof. Cope reached here from South America, but the race con- 

 tinued 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. Christ- 

 opher Chain and Saba Banks.' By Prof. J. W. Spencer, Ph.D., M.A., 

 F.G.S. 



The St. Christopher (St. Kitt's) ridge rises from 2000 to 2800 feet 

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

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

 serrat, where a depression reaches 2592 feet, and between Statia 

 (St. Eustacius) and Saba, where it reaches 1200 feet. Relics 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 ele- 

 vation to about 3000 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. Another depression 

 to 40 or 50 feet filled up these ravines. Then came final re-elevation, 

 and it is possible that a downward movement is now in progress. 



