AGASSIZ: BAHAMAS. 103 



Hogsty Reef. 



Plates I, and II. 



Hogsty Eeef is a small atoll, irregularly elliptical ; its longer axis is 

 something more than five miles and its shorter about three at its widest 

 part, measured approximately from the limits of the 20 fathom line. 

 As will be seen from the deep soundings to the northwest and south- 

 west of the reef, there is a depth of nine hundred and five fathoms not 

 more than four miles and a quarter from the 100 fathom line to the 

 northwest of Northwest Cay, and as great a depth as twelve hundred 

 and eighty-one fathoms somewhat less than four miles to the south of 

 Southwest Cay. The accompanying sketch of the reef (Plate II. Fig. 1) 

 I owe to the kindness of Captain "Wharton of the British Admiralty. It 

 has been slightly .modified from the soundings taken by the " "Wild 

 Duck " off the northeastern face of the reef. Quite an extensive pla- 

 teau was developed on that side, exteuding the 100 fathom line more 

 than a mile to the eastward from the position formerly assigned to it. 

 With that exception, the shelf between the 3 fathom line and the 100 

 fathom line is quite narrow, and the slope most abrupt between seven- 

 teen and a hundred fathoms. It is only on the eastern edge that suc- 

 cessive soundings were taken of ten, eleven, and twenty fathoms before 

 reaching the 100 fathom line. Usually we might strike ten or twelve 

 or perhaps fifteen fathoms, and the next sounding would show no bot- 

 tom with the 50 fathom hand-line. The slope to the south of the atoll 

 is slightly greater than 1 : 2.7, and that on the northern side not quite 

 so steep, 1 : 3.1. (Plate II. Fig. 3.) 



With the exception of the broad triangular shelf on the eastward side 

 of the reef, where the corals extend out fully one mile from the breakers, 

 the annular ring of growing corals is less than a thousand feet wide. In 

 the lagoon itself no heads are growing except those which are found scat- 

 tered between one and a half and two fathoms ; these grow more luxu- 

 riantly as they get within reach of the effects of the last inner line of 

 breakers. Here and there a head is also found in the lagoon in some- 

 what deeper water, but none were seen inside at any distance from the 

 shallower parts of the reef. On the eastern face there is a stretch of 

 corals perhaps a hundred yards in width, of which here and there a mass 

 is exposed to the air at low tide, but as a rule there is a foot to a foot 

 and a half of water at low tide over the shallowest part of the reef. On 

 this narrow shelf and on its lee side are thrown up fragments of corals, 



