116 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
containing small fragments of organisms. Subsequently, dolomite crystals 
were deposited on the coral walls which can now be traced by a dirt 
line. The substance of the coral has been broken down, and its place is 
now taken by a fine gray dolomitic “silt,” in which larger crystals of 
dolomite have formed. On applying Lemberg’s test to a thin section of 
this rock, it is found that, in spite of dolomitization, most of the “mud ” 
in the slide becomes stained, showing that it still consists of a finely 
divided calcite. 
Fie. 9. 
Manco, 290 feet. A much altered cavernous dolomite, whose cavities are now 
nearly filled with large crystals of secondary calcite. > 30. 
After the complete dolomitization of a rock, it is noticed that cavities 
are often filled or partly filled by the further deposition of crystals 
apparently from solution. ‘This deposited material consists sometimes of 
dolomite, in which case the composition of the rock is not much changed ; 
in most cases, however, the material deposited consists of broad crystals 
of calcite. 
Figure 9 illustrates this point, and represents a section of a fragmental 
limestone from Mango at a height of 290 feet. The figure shows that 
the limestone has been thoroughly dolomitized, and as a consequence the 
organisms are largely obliterated, while cracks and cavities have arisen in 
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