AGASSIZ : BKUMUDAS. 251 



Cut in eight fathoms, as it passes out on to the bank becomes hard, and 

 is covered with Thalassia. 



On the inner edge of the reef to the north of Three Hill Shoal, 

 starting from Mills JJreaker Passage, we could observe in the close 

 network of ledge patches no differences between them and those of 

 other localities. The massive corals are perhaps tiner and more nu- 

 merous than elsewhere on the reefs. The Ma,'andrinas and Astrseans 

 are more abundant, as well as the Gorgonians, Algse, and Corallines. 

 The submerged faces of the reef ledges, as examined through the water 

 glass, show no difference from those of similar ledges, such as we see 

 risin<^ from six to seven fathoms of water to a depth of two or three 

 fathoms at low water, on which corals, Gorgonians, Algae, and Coral- 

 lines have not as yet obtained a foothold. In the deeper parts of 

 the interior sounds, in from ten or more fathoms (sixteen at the out- 

 side), the bottom sand is much coarser than we find it in the shallower 

 patches somewhat protected by the reef ledges, or in the reef bights in 

 which patches of sand run in a considerable distance between the ledges. 

 The reef ledges close to the edge, with nearly vertical or very steep sides, 

 in from ten to eleven fathoms, are often separated by deep passages 

 covered with sand, though occasional patches of Gorgonians and Algae 

 or Corallines grow over this bottom, and form connecting bottom strips 

 between the ledges. A considerable amount of dead material accumu- 

 lates at tlie foot of the reef patches and ledge flats, and, according to its 

 position, is being slowly ground into the characteristic bank sand bottom 

 composed of fragments of Millepofes, Corallines, Algae, Gorgonians, and 

 Nullipores. 



The " breakers " known as special rocks on the outer edge of the reef 

 flats, such as Soutliwest Breaker, the Mills Breaker, North and Northeast 

 Breakers, and many others, of which the North Rock is the most promi- 

 nent, are the remnants of islands and islets or of ranges of a?olian hills 

 which once rose upon the outer reef flats, and surroimded the now 

 snuken sounds, the lagoons and waters of the inner part of the Bermudas 

 to the northward of the islands. They have by most observers been con- 

 sidered as owing their origin entirely to the growth of the corals we find 

 thriving upon the sm-face of the ledges which compose these pat.che.s. 



There are also three or four breakers bare at low water between the 

 North Eock and the Pilchard Dicks. The Southwest Breaker is the 

 westernmost of a series of ledges parallel to the south shore extending 

 to the eastward as far as the entrance to St. George Harbor, the geolian 

 character of which can readilv be observed. The inner ledges extending 



