172 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
ANALYSIS OF Rock FROM THE STONE REEF or Кто FORMOSO, 
В. N. BRACKETT, ANALYST. 
Specimen dried at 110° to 115° Centigrade. 
Per Cent Per Cent 
Matter soluble in concentrated hydrochloric acid 35.94 
Matter insoluble in concentrated hydrochloric acid 64.06 
Silica (8105) (nearly all poate сем TH 6000 
Alumina (АО) - . va een, 
Iron (FeO) . Pile 050 
Lime carbonate (Ca00,) ж Кык M АЙОО 
Carbonate of magnesia(MgCO,) = . . . . 497 
Phosphoric anhydride (P. 20%) er U OS 
Magnesia (MgO) . . OR се е о 
POH (Оў — о ads err AE 
Soda (NGO) + Rc 06 
Those on Ignition. +...» Gs 009 
ТО с ee 000 10000 
The analysis shows a rather high percentage of lime, but this lime 
does not all come from the hardening material between sand grains. 
The rock contains many pieces of shells, corals, and other calcareous 
fragments, in addition to the lime deposited between the sand grains ; 
it is not possible to entirely remove all of these shell fragments from 
the material used in the analysis, 
An analysis was made by Prof. L. R. Lenox of the binding material of 
the Mamanguape reef rock. In order that the results of this analysis 
may be compared with that of the Rio Formoso reef rock, the two are 
put here side by side. 
ANALYSES OF THE BINDING MATERIAL or STONE REEFS. 
Rio Formoso rock. Mamanguape rock. 
TOA 0 ee АВ 17.59 
Magnesia (MgO): . . + кы» 2000 2.58 
Equivalent to carbonate of lime (CaCO,) 29.05 31.41 
Carbonate of magnesium (MgCO,) . . 4.97 5.39 
There is, therefore, a striking similarity in the binding materials of 
the two rocks, though the specimens came from reefs more than two 
hundred kilometres apart. 
The hardening of the rock has been produced by the deposition of 
lime carbonate and magnesium carbonate in the sands. When placed 
in acid, the carbonate is soon dissolved, and the sand grains fall apart ; 
second, a microscopic examination of thin sections of the rock shows 
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