ERN. dá 
BRANNER: THE STONE REEFS OF BRAZIL. wa 
silica ; in another instance, the analysis showed 97 per cent of lime 
carbonate and two per cent of silica.” 
The analysis of the Brazilian reef rock, on the other hand, shows that 
it is made up of about two parts of silica to one of lime carbonate, 
including both cementing material and shell fragments. 
It does not scem improbable, judging solely from the amount of lime 
carbonate in the rock, that the cementing materials may have come from 
these same sands, having been dissolved from one part of the beds and 
deposited in another, 
II. Lime carbonate from the ocean. — Hartt long ago suggested that 
the lime carbonate by which the reef rocks are hardened was deposited 
from sea-water.2 Such an explanation, however, can be looked upon as 
satisfactory only when it is accompanied by some explanation of the 
source of the lime, and the method and process of its deposition. It 
may well be objected to this theory that the beach sands in many parts 
of the world are quite as calcareous as those of northeastern Brazil, that 
the surf breaks upon these sands in the same way as it does upon the 
Brazilian beaches, and yet they are not hardened by the deposition of 
lime carbonate. Evidently a satisfactory explanation should deal with 
this part of the problem. 
The theory of the process of hardening by lime carbonate from the 
ocean water is briefly: that the carbon dioxide escapes where the surf 
breaks upon the seashore, just as it escapes from streams at cataracts, or 
wherever a disturbance throws the lime-charged waters into spray, or in 
any way lets the air at the water) Such surf should precipitate both 
lime carbonate and iron, the latter being in solution as ferric car- 
bonate, and being precipitated as ferric oxide. The lime is thought 
to be held in solution as a bicarbonate, and to be deposited as a lime 
carbonate. 
What is the source of the carbonic acid necessary to form the lime 
carbonate with which the Brazilian reef sands are hardened ? 
And why is this process of lithification not a universal one 4 
Т conceive of two methods by which the carbon dioxide might come 
from the ocean. 1. By submarine discharge of CO, of voleanic origin. 
2. CO, derived from the sea-water itself. 
1 Amer. Journ. Sci., April, 1800; XXXIX., p. 249-256. 
2 Ch. Fred. Hartt, Geology and physical geography of Brazil, р. 843. Boston, 
1870. Amer. Nat, June, 1879, XIIL, р. 347-358. 
3 George Murray, in his Introduction to the study of seaweeds, p. 8, points out 
that air introduced into or passed through sea-water carries off carbon dioxide. 
VOL. XLIV. 12 
