Bahamas, studies were made along the western shore of Andros Island and on the 
Yellow Bank directly south of New Providence Island. In Baja California, samples were 
collected along the western side of Espiritu Santo Island, and to a lesser extent on 
adjacent parts of the Baja California peninsula. There is little evidence to suggest that 
either aragonite or high-magnesium calcite is being transformed within the 
unconsolidated sediments that we have investigated. Significant changes have not been 
found in the proportions of aragonite, high-magnesium calcite, low-magnesium calcite, 
and dolomite (where present) in respect to depth below the water-sediment interface in 
cores of sediment. If mineral transformations have taken place, one would expect to 
find a decrease in the proportions of the unstable forms (aragonite and high-magnesium 
calcite) and an increase in the stable forms (dolomite and low magnesium calcite) with 
increasing depth and age. It is suggested that aragonite and high-magnesium calcite are 
not being transformed to low-magnesium calcite because magnesium ions are present in 
sufficient concentration in the water surrounding the mineral grains in the sediment. 
The presence of enough Mg ions in interstitial water prevents transformation of 
aragonite and high-magnesium calcite. Experiments by Taft indicate that if Mg ions are 
present in interstitial water in sufficient concentration so that there is at least one Mg 
ion present in the water for each unit cell of aragonite in direct contact with the 
interstitial water, transformation of the aragonite to low-magnesium calcite does not 
take place. The concentrations of both magnesium and calcite ions is generally greater 
in interstitial water in sediments that we have investigated than in the overlying 
seawater; thus transformation of aragonite and high-magnesium calcite would not be 
expected to occur under existing conditions. In places in southern Florida, and adjacent 
to the west side of Andros Island, the carbonate sediment particles themselves, 
excluding interstitial water, generally contain more Mg than can be accounted for in 
terms of the proportions of high-magnesium calcite. In southern Florida, some of the Mg 
is probably associated with dolomite, which is present in small but highly variable 
proportions. Adjacent to the west side of Andros Island, however, dolomite appears to 
be lacking and yet there is still more Mg than can be accounted for by the presence of 
high-magnesium calcite, It seems likely that some of the excess Mg is associated with 
aragonite. Where very fine (less than 0.001 mm) particles of aragonite are abundant, 
Mg is generally present in excess. It is suggested that Mg ions tend to be concentrated 
on the surfaces of aragonite particles, and that the excess Mg associated with fine 
particles reflects that increased ratio of particle surface area to mass. We have found 
dolomite in unconsolidated carbonate sediments that we have studied only in southern 
Florida. In Florida, the dolomite forms from zero to about 15% of the total carbonate 
material present in the sediment, and forms a maximum of about 2% of the total 
material present in the sediment. Where the proportion of dolomite to total carbonate 
material is highest, there is generally a large proportion of non-carbonate material 
present, such as quartz sand. In southern Florida, some of the dolomite is detrital and 
apparently has been set free by disintegration of limestones. However, many of the 
dolomite grains appear to have overgrowths that have formed very recently. Much of 
the carbonate material in unconsolidated sediments that we have studied has probably 
been secreted by organisms. However, it is suggested that particles that have formed 
by direct chemical precipitation under inorganic condition sand have not been reworked 
(aggregated into fecal pellets, etc.), will be generally smaller than about 0.010 mm, 
and that the proportion of sediment with particle dimensions less than 0.010 mm forms 
a rough upper limit of the maximum proportion of the sediment that could have formed 
by inorganic precipitation. Radiocarbon age dates for different fractions of 
unconsolidated carbonate sediments reveal that carbonate carbon and organic carbon, 
within a given sediment sample, tend to yield different ages. This suggests that the 
individual components of carbonate sediments are heterogeneous in age, and that a 
radiocarbon age date for a given sample merely reflects a kind of average age for all of 
the components. Most of the carbonate sediments that we have studied that have 
