114 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY, 
form the coral sand beaches, or the greater or less fragments which cover 
the reef flats. The negro heads occurring on the edge of some of tho 
flats (Plate VIII.) are all composed of beach rock, and remain as monu- 
ments of the former extension of the beach rock. Тһе reef flats are 
strewn with the dead corals and shells which once constituted this coarse 
beach rock. Тһе beach rock where it still stands is eroded, deeply 
pitted, and honeycombed by the action of the sea, and it resembles lime- 
stones similarly acted upon in other coral reef localities. The beach rock 
conglomerate of the Three Isles is however extremely coarse, made up 
of fragments of oyster shells and of all kinds of corals, once cemented 
together, but disintegrated by the work of the sea. Here and there a 
small vertical bluff of this conglomerate is left standing, showing its 
thickness and the height to which it was elevated above high-water 
mark (Plate XX XIII.). 
I was at first puzzled with the mass of dead corals and of fragments 
of larger blocks left strewn over the reef flats (both on the inner and 
outer reefs), in from two to three feet of water at average low tide. The 
presence of negro heads, remnants of the former elevated coral reef, 
and of negro heads the remnants of former long stretches of elevated 
coral beach rock conglomerate, give us a ready explanation that their 
presence on flats where the sea could not have transported them is due 
to the disintegration and erosion of the coral reef and of the conglom- 
erate when they extended over the surface of the reef flats. 
On Plate XXX. of the Great Barrier Reef (see p. 49), Mr. Kent has 
given a view of huge masses of consolidated coral rock torn off, as he 
says, from the outer edge of one of the Capricorn Island group, and 
hurled far wp on the face of the level platform reef. He called these 
huge masses “ Nigger heads.” Jukes rightly considers them as indicat- 
ing a former elevation, and I fail to see that they show “ direct evidence 
of subsidence rather than of elevation," as is stated by Kent, page 50. 
The throwing up of such huge masses of coral rock is well known to 
5 
occur in all coral reef regions. Ihave given figures of similar huge masse 
of rock washed up by hurricanes in the Bahamas. But, as Kent well 
says, these phenomena “ are mostly associated with the cyclonic storms 
that, during the prevalence of the northwest monsoon, occasionally 
sweep the reefs with irresistible force, though fortunately over limited 
areas." The Italics are mine, and attention is called to the “limited 
areas” as the explanations given by Kent will not explain the occur- 
тепсе on these grounds of “nigger heads" on the edge of so many 
1 Agassiz, Bahamas, Bull. Mus. Comp. Zoól., XXVI. No. 1, Plate XXIV. 
