AGASSIZ: BAHAMAS. 137 



exception of the edging reef on the west side of the Great Bahama Bank, 

 on the east face of the Gulf Stream, we find the bank wholly bare of 

 coral heads. It is one wide expanse of marl and of coral or coralline 

 sand to the west of Andros, and to the north or northwest as well as 

 west of the line from Andros Island to Cay Lobos. To the southeast 

 of the termination of the Tongue of the Ocean the whole surface of the 

 bank is dotted over with an innumerable mass of rocky heads, forming 

 a wide field of seolian rock ledges, separated by narrow channels of from 

 two to three fathoms of water or less, through which only small bouts 

 can navigate. This field extends almost to Nurse Channel on the south, 

 and occupies a large triangular area reaching to the southern edge of the 

 Jumentos Cays. Many of the heads are covered with coral growth. 

 There are similar but more widely separated patches of rocky heads on 

 Columbus Bank, and another extensive area flanking the southern edge 

 of the bank from north of Blue Hole Point to Lobos Cay. In the dis- 

 trict to the north of the line from Blue Hole Point to Diamond Point 

 these patches are met with nearly forty miles from the edge of the bank. 

 Another important patch of coral heads is found to the west of the south- 

 ern end of the Tongue of the Ocean, south of Andros. 



In addition to the Middle Ground southeast of Xew Providence, there 

 is a band of rocky heads occupying the centre of the bank to the west 

 of Xorman Cay, and extending south till it reaches the sand bores to the 

 east of Green Cay. Over the greater part of the rest of the bank the 

 disintegration and reduction of the heads and islands and islets have 

 been so complete as to leave the surface covered only with aeoliau sand 

 and fragments in various stages of destruction, from the finest impal- 

 pable powder to fine sand, coarse sand, and flakes of coralline algae from 

 an eighth to a quarter of an inch in length. 



On the smaller banks, the western and northern edge of Little Bahama 

 Bank north of Bahama Island is occupied in part by heads, and the edge 

 between Settlement Point on Great Abaco and Carrion Crow Harbor is 

 fairly covered with heads between the few islands and islets reaching 

 the surface. On the eastern edge of the bauk the heads are interspersed 

 between the cays, and nowhere form such a peculiar ground as the Mid- 

 dle Ground of the Great Bahama Bank. On Crooked Island and Caicos 

 Banks the sunken heads are limited to a comparatively small area ; in 

 the former to the west side of the bank between Fish Cays and Castle 

 Island, and in the latter to the area of the bank south of Ambergris 

 Cays to South Rock and Swimmer Rock, and along the western edge 

 of the bank. On Mouchoir and Silver Banks there is but a small area 

 where coral heads are found. 



