METASOMATOSIS 139 



12.5%. Assuming that a dolomitic mass resulting in this way 

 is of the same bulk as the original limestone, this shrinkage 

 must manifest itself in the production of interstitial rifts and 

 cavities, such as do actually occur in many dolomitic lime- 

 stones, as those of the Ohio Trenton formations. The principal 

 objection to this theory lies in the difficulty of accounting for 

 the large amount of magnesia in solution; whence its source, 

 etc. The same objections apparently apply to the explanation 

 given by M. C. Klement.^ This writer describes a series of 

 experiments in which solutions of sodium chloride and magne- 

 sium sulphate were made to act upon pulverized calcite and 

 aragonite. From the results obtained, he concluded that dolo- 

 mite is formed by the action of sea-water, concentrated in en- 

 closed basins and heated by the sun, on the aragonite deposited 

 by marine organisms, in such a way that a mixture of carbon- 

 ates of calcium and of magnesium is first produced, which is 

 subsequently converted into dolomite. 



Still another theory regards the dolomite as a residuary 

 product formed by the leaching out of the lime carbonate from 

 beds of impure, slightly magnesian limestone, leaving behind the 

 less soluble magnesian carbonate. The amount of material lost, 

 and the consequent contraction of the original beds, must neces- 

 sarily vary with their purity; but in any case where the residual 

 mass has reached the condition of a true dolomite, the propor- 

 tional loss must have been enormous, since in no cases are un- 

 altered sediments known to contain more than 4 or 5% of mag- 

 nesian carbonate. This theory in its turn is apparently rendered 

 invalid by the presence in the dolomites of very perfect casts of 

 fossils which have undergone no crushing or distortion what- 

 ever, and which show that the beds as a whole, so far from 

 having undergone a shrinkage of 95% and upwards, are of es- 

 sentially the same bulk as when laid down.^ The recent suggestion 

 of Professor J. W. Judd, on this point, seems in the present 

 state of knowledge most satisfactory. From an examination of 

 the deep borings obtained on the Atoll of Funafuti' he was led 

 to conclude that the pronounced dolomitization found in the 

 deeper lying rocks of the reef was due, as in the cases above 



^ Bull, de la Societ6 Geologique de Beige, Tome IX, 1895. 

 2 See The Magnesian Series of the Northwestern States, by C. W. Hall 

 and F. W. Sardeson. Bull. Geol. Soe. of America, Vol. YI, 1895, p. 167. 

 » Beport of Coral Reef Committee, Royal Society of London, 1904, p. 387. 



