Volcanic Disturbances in West Indies 



2 39 



calcareous formations are found notably 

 at Sainte-Anne in the southwest penin- 

 sula of the island, which makes a great 

 salient in the Strait of St Lucia, and of 

 Vauclin to the windward of the main 

 mass of volcanic rocks. The calcareous 

 formations occur to the seaward of the 

 igneous rocks not only in the vicinity of 

 Sainte-Anne, but along the east coast 

 through the districts of Marin and Vau- 

 clin almost to La Trinite. They form 

 in this vicinity the eroded plateau of 

 Pain de Sucre, and the Monies of Cype, 

 Bataille, Flambeau, and others, the sum- 

 mits of which are crowned by blocks of 

 carbonate of lime, but one everywhere 

 sees overlying volcanic rocks, which also 

 occur in the Isle of the Table-au-Diable 

 and Portes-d'Enfer. 



The calcareous plateau or bench 

 which forms the surface of the peninsula 

 of Sainte-Anne is deposited on a massif 

 of volcanic nature composed of a por- 

 phyry with white feldspar in a decom- 

 posed brick-colored matrix and very 

 friable, owing to oxidation. These rocks 

 are much jointed, like prismatic basalts. 

 The superposed limestones have a thick- 

 ness of 25 to 30 feet and are marked by 

 horizontal bands. These calcareous 

 formations are secondary and parasitic, 

 however, for the main mass of the island 

 is composed of volcanic material which 

 has been piling up since the beginning 

 of Tertiary time. 



The volcanic rocks, which are pre- 

 dominantly of an andesitic nature, are 

 of several ages and varieties. The older 

 geological writings on the island, writ- 

 ten before the present processes of classi- 

 fication had been adopted, classif y them 

 as trachytes, phonalites, and porphy- 

 ries. The oldest of these are said to be 

 trachytes of Miocene age, which are 

 found in the southern peninsula. Re- 

 ported as covering these are porphy- 

 roids, quartzites, porphyrites, and por- 

 phyries of Pliocene age in the central 

 part of the island. The rocks so far 

 mentioned are those exposed near the 



base of the volcanic piles. These are 

 covered by great thicknesses of tuffs and 

 later eruptive material, especially on 

 the west side. The general surface of 

 the volcanic rocks has also been thor- 

 oughly saturated by earth water and 

 the minerals of their rocks decomposed, 

 so that the rust line or zone of oxida- 

 tion (regolith) is exceedingly deep. 



The Pleistocene and recent eruptions 

 seem to have been entirely of a pumi- 

 ceous nature, and cover all the country 

 to the north and notably in the Riviere 

 Fallasse. Elsewhere in this Magazine 

 Mr. J. S. Diller has published the re- 

 sults of his petrographic studies of rocks 

 collected by the writer from the island, 

 which show that the older rocks from 

 the base of Pelee and Carbet are hy- 

 persthene and horneblende-hypersthene 

 andesites, and the material of the later 

 eruption hornblende- andesite pumice, 

 while the later crater material of Carbet 

 is dacite. Again, much of the material 

 which we now call tuffs exposed in the 

 same places are old mud flows or banks 

 or layers of ashes (lapilli) which have 

 been partially consolidated by the per- 

 colating moisture. 



There is no evidence in the southern 

 and eastern portions of the island of any 

 volcanic activity within historic times. 

 Omitting from further consideration the 

 older southeastern divisions, the north- 

 western peninsula alone further con- 

 cerns the present story. 



The Pitons of Carbet and Pelee are 

 the nipples of a pair of twin volcanic 

 mountains which rise from 9,000 to 

 10,000 feet above their subterranean 

 base. The 4,000 or 5,000 feet of these 

 mountains exposed above the sea are 

 everywhere composed of exactly the 

 same mineral material ejected during 

 their long volcanic history, but varying 

 somewhat in form. At places in the 

 neighborhood of Fort de France and St 

 Pierre up to a height of 2,000 feet 

 some of the rocks are massive crystal- 

 lines, which undoubtedly were origi- 



