1913.] NATURAL SCIENCES OF PHILADELPHIA. 607 



been transported a considerable distance would be explained by the 

 existence of such currents. The Cassada Garden gravels, as I saw 

 them at the type locality, occupy depressions in the general surface, 

 where they have accumulated, and they also occur as low hills or 

 mounds above the general surface. They may represent local 

 channel or even shore deposits when the sea occupied this central 

 plain. More to the east, in the bays that would be formed by such a 

 depression, the Friar's Hill gravels and marls might have been locally 

 formed. The general occurrence of marine shells up to 125-150 feet 

 above sea level, wherever either in the Central Plain or in the 

 volcanic region to the southwestern part of the island the surface 

 soil was exposed by cultivation, is a character of the geology of the 

 island that at once strikes the observer. And from this higher 

 elevation down to the sea level such occurences of sea shells are com- 

 mon all over the island. In the Central Plain the form of surface 

 characterizing a raised beach has not been preserved, but nearer the 

 sea level there are definite raised beaches, some of which were ob- 

 served by Purves and named the "horizontal marls." They no 

 doubt had an origin similar to that of the salt pond and mangrove 

 swamp deposits that are still forming. But the marine shells of the 

 older submergence were in large part or entirely the same species as 

 those of these later deposits. And since the greatest depression of 

 the island during which these shell beds of this submergence were 

 laid down, the general movement of the island has been upward. 

 Indeed, old maps like that accompanying Nugent's paper, compared 

 with present conditions, would indicate that this upward movement 

 is still going on. Evidence of the submergence is to be seen not only 

 in the marine shells found in the soil; the underground water from 

 the region of the Central Plain carries a large percentage of sodium 

 chloride. In wells in this Central Plain and in the water from 

 springs in this region the amount of sodium chloride is so high as 

 to become characterictic of the water of the region. Thus at Gam- 

 ble's Spring it amounts to 1137 parts in 100,000, as determined from 

 an analysis made in 1906, and at Gunthorpe's well, according to an 

 analysis made in 1905, the sodium chloride content rose to 1458 parts 

 per 100,000.^^ At Cassada Garden the sodium chloride content in 

 the water is much less— 390 parts per 100,000. Away from this Central 

 Plain depression the amount of sodium chloride is found to decrease, 

 and this is a characteristic of the limestone district; for instance, at 



15 "The Water Supply of Antigua," by H. A. Tempany, West Indian Bulletin, 

 Vol. XII, No. 4. 



