Vol. 57.] PHYSICAL DEVELOPMENT OE ANGUILLA, ETC. 521 



its kind, dissecting the Antillean chain, entirely cutting off the 

 sunken plateau of the Virgin Islands to the westward.^ 



The St. Martin plateau has a length of 75 miles and a maximum 

 breadth of 45 miles, with an area of about 1800 square miles. 

 The mountainous islands of St. Martin and St. Bartholomew rise 

 as backbones of the sunken mass, while Anguilla and smaller islets 

 represent the unsubmerged portions of the coastal plains, which latter 

 are now generally covered with nearly 200 feet of water. Thus 

 we have here a repetition of the topographical features of the 

 Antigua-Barbuda mass. 



Anguilla is 15 miles long, with Scrub Island, a disjointed ex- 

 tension of it. Its greatest breadth is 3 miles. The north-western 

 side is characterized by cliffs, often vertical, as the waves are 

 encroaching upon its shores. These cliffs are indented by several 

 short cirques. They rise to an elevation of 150 feet, and at one 

 point the summit reaches a height of 213 feet. The slightly un- 

 dulating surface slopes down to the south-eastern shores, forming a 

 peneplain. 



In the centre is a broad depression, locally called The Valley, 

 trending north-westward, but somewhat lower than its rim. 

 The drainage being underground, there are no surface-streams 

 over these limestone-plains, which are but thinly covered with 

 soil. From a point midway along the coast, is an interrupted 

 chain of islets and keys (called Seal Eocks) extending westward 

 to Dog Island, and enclosing Crocus Bay. This is one of the most 

 interesting features of the region, as it suddenly becomes a very 

 deep amphitheatre at the head of a valley indenting the margin of 

 the submarine plateau. From the col, at the head of Crocus Bay, 

 another valley crosses the sunken banks in the opposite direction, 

 extending to a deep embayment in the Atlantic side of the sub- 

 marine plateau. 



Dog Island (rising to a height of 80 feet) and Scrub Island (to 

 50 feet) are the most prominent outliers of the Anguilla group. 

 The islets north of Crocus Bay are low, and partly covered with 

 sand, while others are reefs, in part exposed to view upon the 

 breaking of the surf. 



St. Martin has a triangular shape, with diameters in each direc- 

 tion of 9 miles. The eastern two -thirds is compact in form, with 

 its surface composed of narrow mountain-ridges or isolated points, 

 separated by relatively large valleys. From the foot of the eastern 

 side of the mountains, the surface slopes to form the remains of a 

 base-level of erosion. The highest point has an altitude of 1360 feet, 

 while others attain elevations of 1096 and 919 feet respectively. 

 The mountainous part of the island is indented by bays, across the 

 mouths of which the sea has cast up sand-beaches, as those of 

 Flamand Bay and of Philipsburg, upon which the town is situated. 

 Here the bay is used as a salt-pond, but borings in the underlying 

 soil show that the silted-up valley is more than 60 feet deep. It 



1 See U.S. Hydrographic Charts Nos. 40 & 1002, or the corresponding British 

 Admiralty Charts. 



Q. J. G. S. No. 228. 2 n 



