256 



Papers from the Department of Marine Biology. 



grains were covered with an impenetrable film of organic matter; so 

 some mud was dried and powdered in a mortar to break the pieces 

 and form fresh surfaces, but similar results were obtained with this. 



If mud was mixed with an equal weight of calcite, the results were 

 the same as with pure calcite. This mud and calcite on standing in 

 sea-water for 30 days had not all changed to calcite. All these facts 



7.2 7.3 7.4 7.5 7.6 



7.9 8 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 



Fig. 7. — Equilibrium of calcite with Tortugas sea-water. The pH is marked on 

 the abscissa and the alkaUne reserve X 10,000 on the ordinate. 



Fig. 8. — The equilibrium of CaCOa with Tortugas sea-water. Calcite is denoted by black 

 rhombs, aragonite by rosettes, calcareous mud by black circles (no equilibrium), mud and 

 calcite by black dumb-bells, and pulverized coral by white circles. 



