BRANNER: THE STONE REEFS OF BRAZIL. 241 
bend in the shore this reef connects with the beach. The part here 
exposed is only about one hundred and fifty metres long by fifteen 
metres wide. The great reef opposite this point stands well out of the 
water at low tide. Five kilometres south of the mouth of the Rio 
Persininga the coral reef is double. 
At Ponta do Mangue the outer edge of the coral reef is just one kilo- 
metre from the beach. ‘The tide was not very favorable for an examina- 
tion when this reef was visited. The width uncovered was one hundred 
and fifty metres, but at the lowest tides the width is very much greater. 
It stood 1.3 metres out of water, but it is considerably higher at the 
lowest tides, — probably as much as three metres. 
The surface of the reef here is exceedingly irregular and etched, and is 
all dead save the Serpulae and barnacles that grow over the dead corals, 
and the few Porites and Favias and such other forms as thrive in tide- 
pools, Landward of the main wall of the reef the coral rocks rise in 
patches that are separated from each other by a labyrinth of channels of 
various widths. 
A chemical analysis has been made in duplicate of a typical specimen 
of the rock of which this Ponta do Mangue reef is composed with the 
following results : — 
ANALYSIS OF THE Reer Rock FROM Ponta DO MANGUE, STATE 
or ALAGÕAS, BRAZIL. 
Sample collected by J. С. Branner, July 28, 1899. R. E. Swain, analyst. 
No. 1 No. 2 
Calcium oxide (080), +. 7... 46.01 46.03 
Gh (MgO) «vs 60% 7.05 
ion (UU) ar 85 88 
Alumina ABO) dns 56 59 
Bodum (NA) ar ga ec ИД trace 
Carbon dioxide (СОБ) = » . « +. » 4294 42.96 
Silica (9102) ee... 1.29 
Phosphoric anhydride с D п ND 27 ‚26 
Chlorine (Cl) . . p s a 31 28 
Water (HO) er ST S 9 т? 
Tome О ИОВ 20041 
Ifall the calcium present were there as carbonate, and the rest of the 
carbon dioxide as magnesium carbonate, it would be equivalent to : — 
Carbonate of lime (CaCO,) |... <. 98919 
Carbonate of magnesium (MgCO,) . . . . . . 12.98 
1 Probably as chloride. 
VOL, XLIV. 16 
