322 Geological Society: — 



to have probably come from the Carboniferous rocks and one from 

 the Bunter. The Sands contain no Crag fossils. Mr. F. Chapman, 

 A.L.S., determined fossils from some of the boulders, from the 

 fragments of stone found in the Sands, and from the Sands themselves. 

 The last consist of Cretaceous foraminifera. 



2. * On the Geological and Physical Development of Antigua.' 

 By Prof. J. W. Spencer, Ph.D., M.A., F.G.S. 



Antigua and Barbuda rise from the bank which occupies the 

 north-eastern portion of the chain of the Lesser Antilles. The part 

 of the bank on which these two islands are founded is submerged to 

 the very uniform depth of about 100 feet, but from other island- 

 groups it is separated by depressions of 1800 to 2500 feet. The 

 margins of the bank are abrupt and precipitous, and are indented by 

 deep valleys extending to the more profound depressions. The 

 igneous basement-rocks of the island form the south-western 

 mountain- belt. They are porphyritic andesites or porphy rites, with 

 breccias and ashes which dip north-eastward. Associated with 

 these rocks, and probably overlying them, are limestones which have 

 not yet yielded fossils. The second and median belt of the island 

 consists of stratified tuffs, with included marine and freshwater 

 cherts. From the evidence of fossils these rocks may be Upper 

 Eocene or Lower Miocene, and they manifestly are closely related to 

 the rocks which follow them. The succeeding formation consists of 

 earthy marls associated with beds of white limestone, and is appa- 

 rently conformable to the underlying tuffs. A list of fossils is 

 given, from which it is concluded that the beds are of Upper 

 Oligocene age. Next follows a creamy-white, calcareous sand- 

 stone, and then the Friar's Hill Series of conglomerates and marls, 

 resting unconformably on the white limestones, and considered to be 

 of late Pliocene or early Pleistocene age. These are succeeded by 

 the Cassada Garden Gravels, recent marls containing land-shells 

 some of which are extinct, and coral-reefs, none of which are 

 raised. 



An account of the erosion -features of the region is given, and 

 from this the following conclusions are drawn : — The region was an 

 extensive land-surface, probably at.least 2000 feet higher than now, 

 during the Mio-Pliocene period, and was reduced by denudation to 

 a comparatively low elevation before the close of that time. This 

 was followed by a submergence (the Friar's Hill) to a depth of 

 200 feet below the present altitude. At the close of the Pliocene 

 period there was another elevation to an extent probably exceeding 

 3000 feet, as shown by the channels on the submarine plateau 

 between Antigua and Guadeloupe. This did not continue sufficiently 

 long to complete the dissection of the tablelands, and consequently 

 the Antigua- Barbuda mass remains intact. Then followed a sub- 

 sidence culminating in a 75-foot submergence, a re-elevation to 

 100 feet above the present level, when the shallow channels in the 

 submarine bank were formed, and possibly one or two other small 

 movements. 



