240 Scientific Intelligence. 



centage of magnesium carbonate up to 16 per cent; this maximum 

 occurring at depths of 15 and 25 feet, with a falling off between 

 these depths to 12 per cent. From a depth of 25 feet there is a 

 gradual decline in the proportion of magnesium carbonate till 

 50 feet is reached, where only the normal amount of 1 to 5 per 

 cent is present. This latter relation continues from 50 to 637 

 feet. From here down, however, the percentage rises rapidly, 

 so that at a depth of 658 feet the proportion of magnesium to 

 calcium carbonate reaches the limit of 40 to 60. This high per- 

 centage of 40 per cent is maintained to the bottom* (1114^ feet) 

 with small variation (except for two interruptions to be men- 

 tioned), the maximum of 43 per cent being reached at 950 feet. 

 Exceptional conditions were noted twice : between 819 and 875 

 feet, the proportion of MgC0 3 varies widely with a minimum of 

 4'8 per cent at 826 and a second of 20*6 per cent at 866, and a 

 maximum of 28*5 per cent at 855 feet. Again, between 1050 

 and 1097 feet there is a falling off, with a minimum of 26*63 per 

 cent at 1061 feet and 30*7 per cent at 1080 feet, and a maximum 

 of 39*4 per cent at 1070. These wide variations remain unex- 

 plained. 



In regard to other constituents in the rock, it may be briefly 

 stated that the amount of organic matter in the samples examined 

 was found to be extremely small; at depths below 100 feet quite 

 inappreciable ; insoluble inorganic matter was also shown to be 

 almost completely absent, as is true in general of coral reef rocks 

 not formed near volcanic masses. The amount of phosphates 

 present was in all cases minute and often quite inappreciable. 



The chief interest in regard to the facts stated centers in their 

 bearing upon the important problem of the dolomitization of 

 limestone rocks. This subject is discussed with much thorough- 

 ness by Professor Judd. Attention is called to the established 

 fact that the amount of magnesium carbonate present in living 

 corals is small. The greater solubility of the calcium carbonate, 

 however, tends to increase the relative amount. The rapidity of 

 the leaching-cut process depends upon the special conditions of 

 temperature and pressure, and further varies widely with differ- 

 ent organisms, being greater with those (as the algae) in which 

 organic matter is present to considerable amount. 



This process of leaching-out seems to offer an adequate explana- 

 tion of the increase in the magnesium carbonate up to 16 per 

 cent, which as stated was observed in the upper part of the cores. 

 The much greater rise in the proportion from a depth of 637 feet 

 to the bottom, reaching a maximum of 43 p. c. at 950 feet, requires 

 another explanation. Here, moreover, as shown by the examina- 

 tion by Dr. Cullis mentioned below, the mineralization, slight 

 above, is prominent, the cores are fairly solid and distinct crystals 

 of dolomite are formed to a greater or less extent throughout the 

 mass. 



The author's views can best be presented by quoting his words. 



* Normal dolomite calls for 45 65 per cent. 



