302 PROF. SPENCER ON THE GEOLOGICAL AND [ Aug. 1902, 
IX. Summary anp ConcLusIons. 
From Dominica to Grenada the Windward Islands are underlain 
by a basement of trappean rocks, the same as in Guadeloupe and 
Antigua, where they occur beneath the early Tertiary formations. 
Upon this foundation the older igneous tuffs, accumulated below sea- 
level, may be seen. The volcanic ridges surmounting some of these 
deposits belong to a late period—Pleistocene, or not older than the 
late Pliocene; but volcanic activity has continued down to the present 
time. There are at least two formations of tuffs. The newer is 
derived from the débris of older beds, and contains waterworn gravels 
or boulders, with the bedding more or less disturbed. The lower 
series cannot be newer than the earlier part of the Tertiary Period. 
Upon their denuded surfaces are nearly horizontal beds of stratified 
waterworn gravels, which in turn have suffered great denudation. 
These occur up to an elevation ot 300 feet, or perhaps more. From 
their geological relationship, they have been correlated with the 
Lafayette Formation of the American continent—provisionally 
assigned to the close of the Pliocene Period. 
Lying in valleys excavated out of the surfaces of the older gravels 
is a calcareous marl, with some rounded pebbles, 30 feet thick, 
containing a fauna almost wholly, if not entirely, living at the 
present day, with only a suspicion of older types. This coral- 
limestone has been weathered away, except in protected places, 
showing the enormous denudation that has taken place since its 
elevation. It was not seen at more than 100 feet above the sea. 
The same formation recurs in Sombrero, Anguilla, St. Kitts, Guade- 
loupe, and Barbados. 
Since the Coral Epoch, there has been another subsidence, with the 
accumulation of a second grayel-series, which often rests upon the 
lower gravels, or even lower deposits, where the coral- and the older 
eravel-beds have been washed away. ‘This formation may be corre- 
lated with deposits in similar positions in other islands, and with 
some stages of the Columbia Series of the American continent. The 
overlying tufaceous earths represent another stage of the geological 
series. 
The raised terraces or base-level plains dip outward from the 
mountain-mass, and are evidence of the local elevation, with defor- 
mation, which occurs immediately adjacent to the foci of recent 
volcanic activity, but does not extend beyond the mountain- 
districts. 
So far as observations go, the phenomena of the islands to the 
south are similar to those of Dominica. 
The coastal plains are represented in the islands by only traces, 
or the somewhat enlarged shelves, less than 200 feet below sea-level. 
From St. Vincent to the Grenadines the banks have a considerable 
breadth. Some 20 miles south-east of Dominica, and again some 
60 miles east of Martinique, fragments of the submarine Antillean 
plateau rise to within 300 feet of the surface ofthe water: presumably 
these are remnants of ancient coastal plains, dating from before the 
