REVIEWS 817 
If the back coast border of the plateau were continued seaward, the 
borders of the island would lie much beyond the present shore line, 
and from this and other phenomena it is inferred that the former exten- 
sion of the island was considerably greater than the present. There 
are terraces on the submerged slopes of the island similar to those 
above the water, which are in harmony with this view. 
Bordering the plateau below the back coast border there is a coastal 
plain which is nearly continuous. In some places it is narrow, and in 
others it reaches far back into the island. The coastal plain is made 
up of three sorts of formations, elevated reefs, sea margin débris, and 
land alluvium. The coastal plain is more or less terraced by old wave- 
cut terraces, which have since been submerged and are now veneered 
with later deposits. The highest is about 150 feet above sea level. 
Filevated=: reets: occur, at three. levels, (60,;. 25, and 15 feet or less; 
respectively, above sea level. 
The streams of the island belong to two types: (1) the autogenous 
type, with the peculiarities which go with changes of level; and (2) the 
interior streams which drain into limestone sinks. In addition to these 
two types, there is a combination type which results from the 
capture of the interior drainage by streams which flow seaward. 
A topographic map with 250-foot contours and a geologic map 
accompany the volume, and help to make the geography and geology 
clear. 
Geology.— The central mountain axis of the island is made up of 
rocks known as the Blue Mountain series. This series is made up 
chiefly of ‘‘loose or slightly indurated beds of gravel, clay, bowlders, 
and tuffs, with exceptional beds or bosses of hard indurated limestones 
and yellow clay. The rocks are usually of dark color . . . . in strong 
contrast to the glaringly light colors which characterize the succeeding 
formations of the oceanic and coastal series. ‘The material, with the 
exception of occasional limestone beds and a few outcrops of clay 
marls, can be traced to igneous rocks; it was first volcanic ejecta and 
subsequently and successively underwent various degrees of attrition 
and sedimentation 72.0. . (pita). 
This Blue Mountain series constitutes the surface formation of all 
parts of the island which rise above 3000 feet. From exposures at 
lower levels where erosion has removed the overlying strata, it is known 
that the same series has extensive development beneath the younger 
formations, and from the known exposures the series is believed to 
