531 PROP. J. W. SPENCER ON THE GEOLOGICAL AND [NoV. I9OT, 



33. On the Geological and Physical Development of the St. 



Christopher Chain and Saba Banks. By Prof. Joseph 

 William Winthrop Spencer, M.A., Ph.D., F.G.S. (Bead 

 April 24th, 1901.) 



Contents. 



Page 



I. Introduction 534 



IT. Physical Characteristics 534 



III, The Volcanic Formations 536 



IV. The Limestones of Brimstone Hill 536 



V. The St. Kitts Gravels 537 



VI. Date of the Volcanic Eruptions 539 



VII. Notes on Eedonda and Montserrat 539 



VIII. Erosion-Features 540 



IX. Summary and Conclusions as to Changes of Level of 



Land and Sea 541 



I. Introduction. 



The islands of Saba, St. Eustatiiis, St. Christopher, Nevis, Bedonda, 

 and Montserrat form the interrupted extension of the mountain- 

 district of Guadeloupe, constituting a succession of volcanic ridges, 

 surmounting the Caribbean side of the eruptive belt, which is seen 

 to have a breadth, at sea-level, of 35 miles. 



The Saba Banks, situated upon the south-western side of the 

 eruptive backbone of the Antillean chain, correspond to the sunken 

 areas of the St. Martin- An guilla and Antigua-Barbuda banks, upon 

 the eastern side. 



William Maclure's contributions in the early part of the nineteenth 

 century refer to some of these islands.^ Mr. P. T. Clove's paper ^ 

 is, however, the most valuable geological publication on the subject. 

 Locally, Dr. Christian Branch and his father have given much 

 attention to the natural history of St. Kitts, and they kindly 

 conducted me to many points of interest. 



II. Physical Characteristics. 



St. Christopher, everywhere in the West Indies called St. Xitts, 

 with St. Eustatius, called Statia, on one side, and Nevis on the 

 other, form a trisected ridge, fringed by a narrow submarine coastal 

 plain, sunk to a depth of between 80 and 140 feet, which last rises 

 above the floor of the submarine Antillean plateau to a height of 

 between 2000 and 2700 feet or more. Saba is an isolated volcanic 

 cone rising out of equally deep water ; and Montserrat, to the 



1 Journ. Acad. Nat. Sci. Philad. vol. i, pt. 1 (1817) p. 134. 



2 ' On the Geology of the N.E. West India Is.' Handl. k. Svensk. Vetensk. 

 Akad. vol. ix (1870) no, 12. An abstract of this paper appeared in Ann. 

 N. Y. Acad. Sci. vol. ii (1881) pp. 185^92. 



