The island of St. Jago extends in a N.N.W. and S.S.E. direction, thirty
miles in length by about twelve in breadth. My observations, made during
two visits, were confined to the southern portion within the distance of a
few leagues from Porto Praya. The country, viewed from the sea, presents a
varied outline: smooth conical hills of a reddish colour (like Red Hill in
Figure 1 (Map 1). (The outline of the coast, the position of the villages,
streamlets, and of most of the hills in this woodcut, are copied from the
chart made on board H.M.S. "Leven." The square-topped hills (A, B, C, etc.)
are put in merely by eye, to illustrate my description.)), and others less
regular, flat-topped, and of a blackish colour (like A, B, C,) rise from
successive, step-formed plains of lava. At a distance, a chain of
mountains, many thousand feet in height, traverses the interior of the
island. There is no active volcano in St. Jago, and only one in the group,
namely at Fogo. The island since being inhabited has not suffered from
destructive earthquakes.

The lowest rocks exposed on the coast near Porto Praya, are highly
crystalline and compact; they appear to be of ancient, submarine, volcanic
origin; they are unconformably covered by a thin, irregular, calcareous
deposit, abounding with shells of a late tertiary period; and this again is
capped by a wide sheet of basaltic lava, which has flowed in successive
streams from the interior of the island, between the square-topped hills
marked A, B, C, etc. Still more recent streams of lava have been erupted
from the scattered cones, such as Red and Signal Post Hills. The upper
strata of the square-topped hills are intimately related in mineralogical
composition, and in other respects, with the lowest series of the coast-
rocks, with which they seem to be continuous.

MINERALOGICAL DESCRIPTION OF THE ROCKS OF THE LOWEST SERIES.