252 On the Geology of the Key of Somhrtro, IF. 1. 



fathoms) into two passages: the one on the east of the Key 

 called the Sombrero, and the other (of nearly twice the size) 

 called the Anegada passage. The Virgin bank on the west 

 encircles St. Thomas, St. John's, Anegada, and the other 

 islets of the Virgin group. Its nearest point is forty miles 

 from Sombrero, and the deep-water soundings off its edge 

 vary from 140 to 160 fathoms. The opposite bank comprises 

 the islands of St. Martin, St. Bartholomew, and Anguilla ; it 

 approaches within twenty miles of the Key ; and the soundings 

 off its edge vary from 102 to 190 fathoms. The only land ever 

 visible from the Key is that of St. Martin and the peak of Saba, 

 low down on the south-eastern horizon. From its situation, 

 then, this formation, isolated by the deep passage on either side, 

 appears in its origin and development to have been independent 

 of these two banks, and to have been wholly indebted to forces 

 at work within its own limits. 



The Key itself is also surrounded by a submarine bank, the 

 dimensions of which are about three and a half by five miles. 

 The water is bold along the very face of the cliff, as the sound- 

 ings vary from eight fathoms on the leeward sides to fourteen 

 along the eastern side. Thence it deepens very gradually to 

 twenty fathoms, at a distance of a mile or more, and finally to 

 forty-seven fathoms at the outer edge of the bank, while the 

 deep-water soundings off this edge vary from 105 to 150 fathoms. 



§ 2. General Description. — The outline of the Key is irregular, 

 but approaches that of an obtuse-angled triangle. Its extreme 

 length is about one mile ; in breadth it varies from 200 to 1500 

 feet ; and its area is about ninety-five acres. The surface, on 

 the narrow southern third of the Key, forms a general level 

 about forty feet above the sea, whence it slopes very gently, 

 except near the east cliff, down to a broader level of half the 

 former elevation, which occupies the central and northern part. 

 Hundreds of limestone boulders, many of large size, are scat- 

 tered over the rugged surface, especially over that of the slope. 

 There is no beach whatever, the sides of the Key rising abruptly 



