608 PKOP. J. W. SPENCER OJT THE GEOLOGICAL AND [NoV. I9OI, 



coast-line appears to be bordered by a narrow plain, now submerged, 

 but deeply indented by ravines. The eastern side of the mountain- 

 range descends less rapidly than the western side, having larger 

 and more important valleys. 



Grande Terre and Guadeloupe proper are almost divided by 

 the broad bays, called 'Grand Cul-de-Sac Marin' and ' Petit Cul- 

 de-Sac Marin.' They are separated by an isthmus about 3 miles 

 across, which is traversed by a narrow strait (from 100 to 400 feet 

 wide) called Salt Eiver. These shallow bays are more or less 

 obstructed with recent coral-growths. The isthmus is only a few 

 feet above sea-level, but it is bounded by low escarpments about 

 3 miles apart, that on the eastern side being of limestone. 



III. Notes on Guadeloupe peoper and the Basement 

 OF THE Island. 



The oldest rocks in Guadeloupe may be seen along the flanks of 

 the mountains. There are evidently several formations, varying in 

 age from that of the old eruptive foundation to the recent volcanic 

 accumulations, some of the intermediate deposits being of mechanical 

 origin, derived from the older igneous rocks. There are also a few 

 remnants of calcareous beds. Seen to an altitude of about 1200 

 feet, along the road east of Basse Terre, there is an old conglom- 

 erate composed of angular and subangular fragments of volcanic 

 rocks. Beyond this summit, and at various elevations down to 

 near sea-level, there are recurring exposures of red residual soils, 

 having a depth of more than 20 feet, which have been derived 

 in situ from the old eruptive rocks. Near Trois Rivieres is 

 an underlying sandy tuff, in well-marked beds which are thrust 

 up into an anticline. This tuff is probably the equivalent of the 

 yellow tuff and volcanic sand underlying the limestones of Grande 

 Terre, though the beds are not continuously traceable. Two miles 

 north ofCapisterre (which is on the south-eastern coast), and at 

 various points to beyond the isthmus, one may see the interrupted 

 exposures of loams and gravels which constitute a formation more 

 recent than the limestones of Grande Terre. These accumulations, 

 as well as the gravels about Basse Terre and some fragmental 

 remains of limestones, will be referred to again (p. 513). The 

 recurring exposures of residual soils, the loosely compacted tuffs laid 

 down beneath the sea, and the loams and gravels, are due to the 

 relative amount of erosion of the land-surface in late or recent 

 geological times. 



At the northern end of the island, and thence westward to Port 

 Deshayes, are thick beds of compact volcanic tuffs, con- 

 taining numerous small fragments distributed irregularly through 

 the fine materials of the beds, and large boulders; but the strata are 

 often so distributed as to make their dip undeterminable. These 

 same beds are seen, with some interruptions along the western coast 

 to south of B iiill a n t e, where they vary in position from horizontal 

 to an angle of 20°. They rest upon a basement of eruptive rocks 

 with denuded surfaces. The age of these tuffs, and that of the 



