490 PROF. J. W. SPENCER ON THE GEOLOGICAL AND [Nov. I90I, 



30. On the Geological and Physical Development of Antigua. 

 By Prof. Joseph William Wintheop Spencer, M.A., Ph.D., 

 F.G.S. (Eead April 24th, 1901.) 



[Plate XV— Map.] 



Contents. 



Page 



I. Introduction and Early Observations 490 



II. Situation and Pliysical Characteristics 491 



III. The Igneous Basement of the Island 493 



IV. The Seaforth Limestones 494 



V. The Tuffs and included Marine and Freshwater Cherts 494 



VI. The White Limestones or Antigua Formation 496 



VIL The Hodge's Hill Sandstones 498 



VIII. The Friar's Hill Series 499 



IX. The Cassada-Garden Gravels 500 



X. Eecent Deposits - 500 



XL Coral-Eeefs 501 



XII. Notes on Barbuda 501 



XIII. Erosion-Features of the Antigua-Barbuda Region 502 



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



and Sea 504 



I. Introduction and Early Observations. 



The island of Antigua may be taken as a starting-point for the 

 study of the Windward Islands, as within its area of 100 square 

 miles almost all of the geological and geographical features of the 

 region, except the later volcanic phenomena, are developed in such 

 a way as to be easily understood. The only other island comparable 

 for a base of study is Guadeloupe, which furthermore includes all 

 the recent volcanic features on a grand scale, but some other 

 features less easily distinguishable than in Antigua. 



On November 5th, 1819, Dr. Nicholas Nugent, a physician of 

 Antigua, communicated to the Geological Society of Loudon ' A 

 Sketch of the Geology of the Island of Antigua'^; but a * Memo- 

 randum * of this had been sent to Benjamin SiUiman on April 10th, 

 1818, and was published two years earlier in America^ than the 

 fuller London paper, Nugent also sent to the Geological Society 

 large collections of the rocks and fossils, carefully labelled as to 

 their horizons. These remained almost unstudied for over forty 

 years, when P. Martin Duncan made an elaborate study of the 

 corals contained in them,^ which appeared in 1863-64. 



Nugent had a companion in his studies of the island in the 



1 Trans. Geol. Soc. ser. 1, vol. v (1821) pp. 459-75. 



^ Am. Journ. Sci. ser. 1, vol. i (1819) pp. 140-42. The petrified wood of 

 Antigua had even before this attracted attention ; and a notice of a collection 

 made by Pelatiah Perit (of New York) is found a little earlier than Nugent's 

 ' Memorandum,' on p. 56 of the same volume of the Am. Journ. Sci. 



' ' On the Fossil Corals of the V^^est Indian Is.' Quart. Journ. Geol. Soc. 

 vol. xix (1863) pp. 406-58, & vol. xx (1864) pp. 20-44, 358-74. 



