526 PEOI'. J. W. SiPENCEPv ON TSE aEOLOGlCAl AND [KoV. I9OI, 



Broad Bay, up to a height of 30 feet, are the decayed remains 

 of igneous rocks in part resembling amygdaloids, and others are 

 like volcanic ashes, all of a dark greenish or blackish colour. 

 Yolcanic rocks also underlie Dog Island. Thus there is an igneous 

 foundation for all the islands from the western part of Antigua to 

 Dog Island, the last of the chain, along the line, having a north- 

 westerly direction. Beneath the cliffs, and rising scarcely above 

 wave-action, between Eoad Bay and the landing to the east of it, 

 there is a blue clay and also a gritty deposit containing lignite. 

 These are probably the products of decomposition of the finer 

 felspathic tuffs of the mixed series which occur in the other islands. 



IV. The White ok Antioua Limestones and theik Fossils. 



On the south-western flanks of the mountains of St. Martin, 

 as, for example, near Pelican Point, the tuff-limestone series is 

 unconformably overlain by a white limestone-formation. At this 

 point the underlying beds dip 40° north-westward, while the 

 overlying calcareous deposits dip about 15° south-westward. 

 A short distance to the north-west, the same white limestone- 

 formation overlies decayed igneous rocks, and caps the western 

 side of an isolated ridge, while on the eastern side there is an 

 escarpment 150 feet or more above Simson's Inlet. Here the beds 

 dip slightly westward. The limestone in part is massive, while 

 the bedding is not everywhere apparent. At Pelican Point it 

 forms the surface of a plain, 75 feet above the sea. This is very 

 much pitted, and the formation is characterized by numerous large 

 caverns, one of which — Devil's Hole — appears to reach below sea- 

 level. The surface of this rock is partly phosphatized, but no 

 phosphate of lime was found in the shafts reaching to a depth of 

 75 feet, nor in a tunnel drifted in the side of a hill, showing that 

 the phosphatic matter is confined to the surface. The 

 subsequent physical movements are here shown in the slickensided 

 walls, where the planes of slipping dip 75° westward. 



The same limestones also occur a short distance away in the 

 island of Anguilla, which was once evidently a part of the 

 coastal plain extending from the mountains of St. Martin. 

 Tintamarre, an adjacent outlier of St. Martin, represents a 

 fragment of the dissected coastal plain. It is underlain by the 

 same white limestones. While only a few undeterminable shells 

 have been found in St. Martin, fossils occur in both Anguilla and 

 Tintamarre ; consequently these islands afford better localities for 

 determining the age of the white calcareous formations. 



Another limestone occurs at the eastern end of Point Blanche. 

 It has a creamy colour, with a homogeneous texture, being really 

 a hardened calcareous sand (locally called 'sandstone'), which is 

 used for building purposes. It forms a cap 15 or 20 feet thick, 

 unconformably above the silicified limestones, and dips at 35° 

 south-westward. The surface is carved, by the action of the waves 

 dashing upon it, into excellent miniature examples of the forms 



