514 PEOF. J. W. SPENCEE ON THE GEOLOGICAL AND [NoV. IQOI, 



depressions show the surface of the country to have been greatly 

 denuded. There are evidently two formations overlying 

 the volcanic tuffs, each of loams and gravels with the pebbles 

 of the upper series of smaller size, while the lower gravels are 

 coarse and exposed only in sections along the coast or in the interior 

 of the hills where access has been had to them. The upper deposits 

 form a mantle over both the high and low ground, and have not 

 been nearly so much denuded as the lower. Between Petit Bourg 

 and Salt Biver, these mechanical formations rest upon white lime- 

 stones, rising only in a few j^laces above the sea. All the strata, 

 whether limestones or loams and gravels, lie almost horizontally, 

 dipping very slightly north-eastward. Accordingly, the outlying 

 limestones west of the isthmus are the equivalent of those of Grande 

 Terre, but separated by the broad shallow depression, occupied by 

 the isthmus (2 or 3 miles across), excavated when the country was 

 reduced to near the base-level of erosion, before the deposition of 

 loams and gravels which lie on it. From ^11 these facts it appears 

 that both members of the Petit-Bourg Series are relatively of late 

 origin. 



The occurrence of these two mechanical deposits, composed of the 

 same materials, is only a rej etition of the phenomena of the Lafayeti;e 

 and the Columbia formations of the coastal plains of North America, 

 where the component materials can scarcely be distinguished, except 

 by the unconformity, etc., which represents an enormous physical 

 break in their succession. The accumulation of the Lower Petit- 

 Bourg Series in the same ])osition as that of the Lafonde is v\hat 

 might be expected, owing to their both being the succeeding beds 

 deposited upon the surface of the country, subsequent to the 

 denudation of the Miocene-Pliocene Period. The Petit-Bourg gravels 

 are situated at the foot of hills, supplying eruptive materials for 

 the loams and pebbles, while the Lafonde gravels are derived from 

 limestones of the small islands remaining above water during the 

 submergence of this epoch. Prom the erosion-features it is mani- 

 fest that the upper series of loams and gravels are very much 

 newer than the lower, and occupy the same horizon as the Cassada- 

 Garden Series of Antigua, or the Columbia Series of the American 

 continent.^ 



The loams appear to be derived from the pre-existing residual 

 soils, such as those mentioned, and the upper loams and gravels 

 seem to have been the material of the lower series worked over 

 again. 



In the weatherworn terraces above Basse Terre, upon the 

 south-western side of Guadeloupe proper, thin beds of gravel occur 

 up to an elevation of 250 feet. This superficial mantle has not 

 been connected with the Petit-Bourg Series, but it has the general 



^ These are also i-epresented by the Zapata Series of Cuba, and the Liguanea 

 of Jamaica. Furthermore, a cori-esponding formation is fouiid in St. Martin, 

 St. Kitts, etc. 



