196 bulletin: museum of comparative zoology. 



two islands which throw the greatest light upon the age of the 

 vulcanism of the Caribbees. 



In Antigua the older massive volcanic rocks constitute a high moun- 

 tainous region on the south side of the island, while to the northward 

 for miles these are overlapped by a vast thickness of stratified tuffs, 

 evidently the ejecta from the vents of which the massives are the 

 remnantal stocks. This material must be thousands of feet in thick- 

 ness. It contains beds of thin lime deposits of marine origin, including 

 a bed of older massive consolidated crystalline limestone less than ten 

 feet in thickness, and an old coral reef. Towards the north end of the 

 island the tuffs are overlain by conglomerates grading up into chalk 

 marls with fossil MoUusca of possible Miocene age. In the tuffs there 

 are also beds of chert with vast quantities of fossil wood, land shells, and 

 silicified reef building corals (but no reef rock), which also extend into 

 the marls. Finally there is a small area of elevated reef rock. Of 

 these stratified formations none in my opinion, except of the Orbitoidal 

 crystalline limestone, can be of older age than Pliocene or late Miocene. 

 The latter may possibly be Vicksburg — an opinion based upon the 

 occurrence therein of Orbitoides and JSTummulinse. described by T. 

 Rupert Jones. Upon the erroneous correlation of others he referred 

 these beds to the Miocene, but they are older in age than the Bowden 

 beds of Jamaica " Miocene " with which they have been confused by 

 many writers. These facts show that the volcanic tuffs of Antigua 

 were being formed before the Vicksburg epoch, and that the Caribbean 

 vulcanism was then active. 



In Guadeloupe we have somewhat similar evidence concerning the 

 evolution of the volcanic range and the mass of sedimentaries. This 

 island is composed of two parts of about equal area, separated by a 

 shallow creek. Riviere Salee. The most western of these islets (Basse 

 Terre) is a typical volcanic pile of the main Caribbee chain, and is 

 thoroughly mountainous. The most eastern area, Grande Terre, is an 

 elevated cut plain, composed of sedimentary formations of Pleistocene 

 age underlain by a platform of volcanic tuffs, etc., derived from the 

 volcanic debris of Basse Terre. Still to the eastward of Grande Terre 

 is the small island of Desirade, composed entirely of organic material, 

 which, wath several other islets, stands above a shallow submerged plat- 

 form extending out from the sonth cast end of Grande Terre and Basse 

 Terre. To the southward of Grande Terre is the island of Marie 

 Galante. This island is of the same topographic and geologic type as 

 Grande Terre. 



