AGASSIZ: BAHAMAS. 165 



sidered as the remnant of the former extension of the north coast of 

 Honduras : it is remarkably clear of coral patches. With the exception 

 of a narrow ridge rising to a height of two hundred and ninety feet at 

 the eastward, the greater part of the island is low and swampy. To the 

 northeast of Utilla are the islands of Roatan and Bonacca, both within 

 the 500 fathom line. Bonacca (Hydrographic Chart No. 396, Admi- 

 ralty Chart No. 1718) reaches to a height of over twelve hundred feet : 

 it rises from the 5 fathom line upon the eastern end of an elongated 

 bank formed by the 100 fathom line. It is surrounded by clusters 

 of coral bars and cays, which are most abundant on the southeast 

 face of the island. Roatan (Hydrographic Chart No. 394) has an average 

 height of three to five hundred feet : its highest point is nearly eight 

 hundred feet. Its northern shore and that of the eastern islets are all 

 skirted by coral reefs, which sweep round the eastern face of the Roatan 

 Bank and extend in irregular stretches along the southeast coast, where 

 the shore is steep to and the reef disappears, the 100 fathom line running 

 close to the western spit of the island. 



The northern part of the Mosquito Bank (the 100 fathom line), which 

 extends nearly one hundred and forty miles to the east of Cape Gracias 

 a Dios, is remarkably free from coral patches and bauks. North of Half- 

 Moon Reef there are only insignificant clusters of coral reefs and bars, 

 forming the Caxones and Vivorilla Cays, to the eastward of which there 

 are a small reef and some insignificant cays designated as the Gorda 

 Bank. 



The submarine scenery of some parts of the West Indies must be most 

 striking. We have first the long line of steep eastern slopes of the Ba- 

 hamas, with the valleys separating them, which rise abruptly from a great 

 submarine plain, extending far to the eastward and constituting the floor 

 of the ocean, from a depth of twenty-five hundred fathoms. This plain 

 extends all the way from the Little Bahama Bank to Navidad, a distance 

 of over seven hundred miles. Then follows the long, unbroken submarine 

 slope extending off Porto Rico to the eastward of the Anegada Channel 

 for a distance of over four hundred miles, with the remarkable sink of 

 more than forty-five hundred fathoms in depth north of Porto Rico, one 

 of the greatest depths as yet discovered in any ocean. Then the valley, 

 over twelve thousand feet deep, which extends south of the smaller east- 

 ern Bahama banks, gradually lessening in depth toward the Old Bahama 

 Channel and flanked on the southern face by the mountains of San 

 Domingo. And finally, perhaps the most striking topographic feature 

 of the West Indian area, the deep valley skirting the southern shore of 



