520 PROF. J. W. SPENCER ON THE GEOLO&ICAL AND [ISToV. I9OI, 



32. On the Geological and Physical Development of Anguilla, 

 St. Martin, St. Bartholomew, and Sombrero. By Prof. 

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

 (Eead April 24th, 1901.) 



Contents. 



Page 



I. Introduction 520 



II. Physical Characteristics 520 



III. The Older Geological Formations 523 



lY. The White or Antigua Limestones and their Fossils 526 



V. The Newer Formations 529 



YI. Mammalian Eemains 530 



VII. Erosion-Features „ 530 



VIII. Summary and Conclusions as to Changes of Level of Land 



and Sea .. 533 



I. Introduction. 



The drowned plateau, standing boldly above the great submerged 

 Antillean ridge, now forming the slightly sunken banks, out of 

 which rise Anguilla, St. Martin, and St. Bartholomew, with some 

 small outlying islands, is a repetition of the Antigua-Barbuda 

 mass ; in size a little larger, drowned a little deeper, more broken, 

 and with its marginal declivities strikingly indented. Sombrero is 

 an isolated feature. 



Apart from the excellent contribution of Mr. P. T. Cleve,^ there 

 appears to be no geological account of the islands ; but the dis- 

 covery of mammalian remains b)^ Edward Cope, among the bones 

 obtained in Anguilla by Mr. Wager Eay, of that island ^ and the 

 study of fossil echinoderms of the same island by Mr. K. J. 

 Lechmere Guppy,^ are important additions to our knowledge of the 

 region. 



II. Physical Characteristics. 



The south-eastern extension of the St. Martin plateau, with its 

 surface covered by only about 200 feet of water, is separated from 

 the Antigua-Barbuda platform by a depression 18 miles across, 

 but its depth beyond 858 feet has not been determined. The 

 valley between the sunken tableland and Saba, to the south, is 

 20 miles wide and reaches a depth of 2934 feet ; while that 

 separating it, on the west, from Sombrero is scarcely wider, with 

 the depth to the ridge crossing it reduced to 1800 feet. Beyond 

 Sombrero is a channel of phenomenal depth, the only one of 



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

 Akad. Yol. ix, no. 12'(1870) pp. 1-48. 



2 First mentioned in a note in Proc. Acad. Nat. Sci. Philad. 1868, p. 313. 



3 * On Tertiary Echinoderms from the West Indies ' Quart. Journ. Geol. 

 Soc. vol. xxii (18b6) pp. 297-301. 



