Yol. 57.] PHYSICAL DEVELOPMENT OF ANTTGUA. 503 



descending waters. As a broad feature of this old erosion, it may be 

 mentioned that the wide shallow harbours, such as Willoughby Bay, 

 Falmouth Bay, and Eive Island Harbour, are only sunken portions of 

 the land-valleys. But between these, whicli were once surrounded 

 by high hills in the form of amphitheatres, and the low interior 

 country, the elevated lands at their heads have been so reduced 

 in height as to form low passes, leaving the sides of the valleys 

 characterized by prominent elevations. 



The broad undulating or rounded features were formed by atmo- 

 spheric agents prior to the deposition of the Friar's Hill Series, 

 which at most covers the old surface by only a thin mantle. 

 Consequently, the island was continuously a land-surface from 

 the early Miocene to about the close of the Pliocene Period, when 

 it was again partly submerged during the Friar's Hill epoch. 

 Throughout this long era, the topography of the region was a 

 mountain-district, bordered by foot-hills of considerable elevation, 

 among which was the adventitious volcano of Drew's Hill, and 

 perhaps later a volcanic outburst at Crosbie's,^ beyond which the 

 coastal plains extended to the edge of the banks north of Barbuda. 



After the Friar's Hill epoch, subsequent erosion produced other 

 characteristics throughout the region. The broad depressions 

 indenting the margins of Antigua were greatly deepened and 

 extended farther into the highlands. These valleys, on the coast, 

 are now drowned to a depth of 40 or 50, and in one case to 80 feet. 

 On the southern coast the channels of Willoughby Bay and English 

 Harbour are distinctly traceable to a depth of 100 feet, and that 

 of Falmouth to 140 feet, within the limits of the less submerged 

 banks. Similar trenches can be traced upon the submarine plains 

 between the two islands, having a depth of 25 or 40 feet, and in a 

 locality west of Barbuda there is one of 100 feet below the surface 

 of the banks, which are themselves submerged only 80 feet. 

 "Where the margins of the submarine plateau have dropped to 

 150 feet and more below the surface of the sea, they show valle}-- 

 like indentations trending to those of the land. One of the most 

 conspicuous occurs west of Five Island Harbour. It reaches a 

 depth of 1290 feet within the line where the banks are covered 

 by less than 150 feet of water. This deep amphitheatre opens 

 out into the broad submarine valley, where the soundings reach 

 over 1900 feet. Broad embayments encroach upon both sides 

 of the plateau between Antigua and Barbuda, thus considerably 

 reducing its breadth. 



I have just mentioned comparatively narrow channels upon the 

 surface of the submarine plateau, and deep indentations into its 

 margin. The former feature may be produced either where the 

 land has no great altitude above the drainage-level, or upon the 

 surface of a high plateau, sufficiently far within its margin for 

 the streams not to be affected by the deep declivity of its edge. 



^ This is a dolerite containing far more pyroxenic elements than that 

 of Drew's Hill, one of the facts which led M. Purves to infer its more recent 

 origin. 



