West Indian Volcanic Formations. — Spencer. 49 
Croix. The rocks are essentially an anclesyte in form of both 
lavas and tuffs. Their surface topography is moulded by at- 
mospheric agents into low mountains and valleys. Overlying 
such a basement in St. Croix and St. Thomas, according to 
Cleve,* there is a conglomerate containing pebbles with Cre- 
taceous fossils. In this region these basement rocks are so 
dissected that their remains constitute many of the islands of 
the Virgin group. 
But in Antigua and Grande Terre of Guadeloupe the 
strata overlying the denuded igneous basement is a sub-aqueous 
re-distributed tuff with some calcareous beds in the upper zone, 
over which rest confonnably the white limestones, a marly 
deposit containing Oligocene corals and shells. f South of the 
Guadeloupe archipelago and Monserrat, the outer islands dis- 
appear, and the writer is not aware of the occurrence of the 
early Tertiary limestones remaining so as to leave evidence of 
the age of the igneous basement, though by its lithological 
•characteristics and the physical features of its ancient surface 
one can hardly be far astray in concluding that they are of the 
same age as the similar formations on the islands to the north. 
In Barbados the Oligocene limestones reappear, but here there 
are no igneous deposits. It thus seems that the whole Carib- 
bean plateau beweath both the volcanic ridges and the lime- 
stone islands is underlaid by an igneous formation dating back 
to the commencement of the Tertiary period at least, if indeed 
these rocks are not as old as those of St. Croix, that is as an- 
cient as the Cretaceous period. 
In St. iMartin, St. Bartholomew and Antigua, the moun- 
tain belts are entirely made up of the denuded rocks of this 
old igneous formation without a covering mantle. So also, 
part of Statia, St. Kitts, Alonserrat, the southern end of Mar- 
tinique, portions of St. Lucia and the southern end St. Mncent 
have their surfaces moulded out of the ancient igneous accum- 
ulations ; but elsewhere in these islands, as also in Guadeloupe 
proper and Dominique, they are covered with volcanic mater- 
ials which constitute more or less of the cones and ridges ris- 
ing to a hight of 3,000 to 4,000 feet. In these mountainous 
* On the Geology of the northeastern West Indian islands. Trans. Roy. 
Sociedad Acad. Sci.. vol. ix. 1870-71. 
t See "Geological and Physical Development" of the various Windward 
islands, in six papers by J. W. Sprvckr, in Quart. Jour. Geol. Sci., vol. Ivii 
(1901), pp. 409-543, and vol. Iviii, (1902), pp. 341-30.5. 
