THE LESSER ANTH.LES. 457 



St. Christopher (St. Kitts) and Nevis may be taken as a typical specimen of the 

 general disposition of this inner or western chain. 



The outer, about equal in length, sweeps round from Sombrero to Barbados. 

 Like the first it describes the arc of a circle, but is disposed exactly north- 

 west and south-east in such a way as to form a tangent to the convexity of the 

 inner circuit. Guadeloupe is thus constituted a double island, belonging partly 

 to one, partly to the other system. A third line, scarcely indicated above the 

 surface, is revealed by Aves and the neighbouring shoals. 



The main chain of the Antilles consist of elliptical lands with their long axis 

 disposed in the same direction as the chain itself. Each island has also its little 

 backbone which again follows the same general curve. The ranges culminate in 

 the three central islands of Guadeloupe, Dominica and Martinique ; but all 

 members of the system are very elevated relatively to their limited areas ; some of 

 the islets even constitute a single cone, rising many hundred feet sheer above the 

 surface, and in their very form betraj'ing their igneous origin. 



In general the mountains consist of porphyries and lavas, and evidently had 

 their origin on a submar.ine fault, whence they rose gradually above the sea. Some 

 are even still growing b}^ the accretion of fresh eruptive matter. 



But the outer range, from Sombrero to Barbados, is not volcanic, or at least 

 the igneous rocks thrust from the marine bed upwards have not yet reached the 

 surface except at a few isolated points. The plateau on which the islands stand is 

 almost everywhere covered with calcareous formations of oceanic origin. Nowhere 

 is the contrast between the two chains more striking than in the twin islands of 

 Guadeloupe, one elevated, bristling with craggy peaks, scored with lava streams, 

 abounding in running waters, the other low, or gently undulated, fissured with 

 crevasses and honeycombed with caves in which the waters disappear. 



But if the calcareous range rests on a rocky bed, the igneous system itself is 

 not exclusively formed of eruptive matter, for these upheaved volcanic islands have 

 also their margins of oceanic origin. Bound the base of the porphyry or trachyte 

 escarpments have been accumulated to a height of over 800 feet great masses of a 

 grey conglomerate, tinged with red and yellow, in which have been embedded huge 

 blocks that have toppled over from the upper slopes. This conglomerate had its 

 origin below the surface at a time when the sea-level was relatively higher than 

 at present. The marine formations deposited at the foot of the volcanoes now 

 stand above the sea in consequence either of a subsidence of the waters or of an 

 upheaval of the land. Should the movement continue, the banks of reefs or cays at 

 present encircling the submerged base of the islands will be seen to rise above the 

 surface, especially on the side facing the Atlantic. 



The composition of the rocks is the same in the still flooded reefs as in the 

 already upraised cliffs ; even in appearance they differ little, though the more recent 

 coralline growths are somewhat softer, and of a less yellowish colour. In some 

 places the conglomerates on the coast are interrupted by lava streams, and both of 

 these formations being contemporaneous, fragments of each are found embedded in 

 the different deposits. 



