522 PROF. J. W. SPEFCEB ON THT! GEOLOGICAL AND [NoV. I9OI, 



lies in the expansion of the mountain- valley as it nears the coast. 

 The mountain-district is characterized by permanent streams, which 

 become torrents with the tropical rains, during one of which I saw 

 8 inches of rainfall in 3 hours. 



The western wing of the island is in part the remains of lime- 

 stone-plains, but it is mostly composed of low flats out of which 

 rise several ridges and hills (the remains of ancient features now 

 connected by recent marine accumulations), the whole forming the 

 border enclosing the island-studded waters of Simson's Inlet, a 

 lagoon from 1 to 6 feet deep. The sunken shelf upon the eastern 

 coast is narrow, and abruptly descends to a depth of 60 or 70 feet, 

 while that on the southern coast soon becomes precipitous, as it is 

 near the margin of the submarine plateau. Where the waves are 

 not encroaching upon the shores, and the water is very shallow, 

 coral-reefs are commonly found. 



The northern part of St. Martin is separated from Anguilla 

 by a depression 4 miles wide, with an uniform depth of 60 to 75 

 feet. This increases to the westward, where within a mile it de- 

 scends precipitously 500 feet into the amphitheatre indenting the 

 western margin of the sunken plateau. Prom this same depression, 

 between the islands, another valley is tra,ceable to the eastward. 

 The question of the drowned valleys will be considered again under 

 the heading of erosion -features (p. 530). 



Tintamarre is a remnant of the coastal plain of St. Martin, 

 though now separated from it by a channel 66 feet deep. It is a 

 limestone-island like Anguilla, with a slightly undulating surface 

 reaching to 90 feet above the sea. Its northern coast is being 

 encroached upon by the waves, producing cliffs, while coral-reefs 

 occur off the southern shores. 



St. Bartholomew is a triangular island about 6 miles long, 

 and is of the same general character as St. Martin. The northern 

 shore sweeps round and encloses St. John's Bay, at the head of 

 which the principal valley of the island is situated. It extends 

 seaward, and becomes a deep bay between the main island and the 

 chain of smaller ones to the northward. The western part of St. 

 Bartholomew rises into a high ridge, while the eastern part is 

 made up of isolated hills, the highest of which is 992 feet. 



The distance between St. Bartholomew and St. Martin is 12 

 miles, with the intervening plain sunk from 80 to 100 feet, but 

 there are several islets or rocks (one of which is 150 feet high) 

 rising above the surface. 



Sombrero is an isolated limestone-rock, 35 miles north-west of 

 Anguilla. Its flat surface is about 25 feet above the sea, and it is 

 everywhere bounded by precipitous cliffs, making the landing very 

 dangerous owing to the prevailing swells in its exposed position. 

 Occasionally the waves break over the whole island, which is less 

 than a mile in length and 250 yards across. But the sunken bank 

 out of which it rises has a length of 4 or 5 miles. Although it 

 is separated from the eastern plateau by a deep depression 20 miles 

 across, yet it is an outlier of it, as it is connected by a ridge which 

 is not reduced to more than 1800 feet below sea-level, while the 



