SKEATS: CHEMICAL COMPOSITION OF LIMESTONES. 115 
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Foraminifera as Amphistegina and Heterostegina and the echinid 
spines. 
The last stage in the dolomitization of a limestone, originally crowded 
with organic fragments, consists in the extension of the invasion of the 
organisms by dolomite crystals and the ultimate destruction of all traces 
of their organic character. This results in the formation of a structure- 
less dolomite consisting entirely of clear or muddily zoned crystals. It 
is often noticed that partly as a result of solution, partly of consolidation 
Fie. 8. 
NGILLANGILLAH, 25 feet. Section of a dolomitized coral. The stereoplasm of 
the coral is now replaced by a dolomitic “silt,” while the external and internal 
walls are represented by “dirt lines.” Opaque “mud” in the cavities remains as 
calcite, and subsequent to its deposition, dolomite crystals, formed from solution, 
have incrusted the walls of the coral. x 30. 
under recrystallization, the rock assumes a more or less cavernous 
appearance. 
A somewhat parallel series of changes under dolomitization can be 
traced in the case of a coral section. Some of these changes can be seen 
on reference to Figure 8, which represents a section of reef-forming coral 
from the dolomitized island of Ngillangillah. 
At a comparatively early stage in the history of the coral, some of its 
cavities were filled quite up to the wall of the coral with a dark “mud” 
