E. W. Skeats— The Formation of Dolomite. 185 



Art. XIII. — The Formation of Dolomite and its Bearing 

 on the Coral Reef Problem; by Ernest W. Skeats, (leo- 

 logical Department, University of Melbourne. 



Introduction. 



The origin of dolomite is a problem which has been dis- 

 cussed for a century. Most of the attempts to solve the prob- 

 lem have been from the experimental and chemical sides. 

 The modes of occurrence of dolomite among calcareous rocks 

 and the geological aspect of the problem have received more 

 attention in recent years. The recognition of the fact that 

 coral limestones are sometimes dolomitized was first due to 

 the observation of Dana* at the island of Metia, but it was not 

 till the detailed chemical examination of the material of the 

 Funafuti bores, f and of limestones from upraised coral islands,:}: 

 was undertaken that it was realized how widespread was the 

 process of dolomitization among coral islands. In the course 

 of these investigations the writer was led to the conclusion that 

 the process of dolomitization of the limestones of coral islands 

 was effected in shallow water,§ and in a later paper|| on the 

 Dolomites of S. Tyrol, he amplified these conclusions. Subse- 

 quent writers on the dolomite problem appear to have over- 

 looked this later paper; at any rate, no discussion of the views 

 therein presented has come under his notice. 



It is, of course, well known that dolomitization may be local f 

 that is restricted to the neighborhood of joints, bedding plants 

 or mineral veins. Dolomites of this restricted occurrence are 

 not here under discussion. On the other hand, "regional" or 

 widespread dolomitization occurs among ancient limestones and 

 among recent coral limestones. Certain dolomites usually asso- 

 ciated with gypsum salt deposits are regional in character, but 

 appear to have been formed in land-locked areas and under 

 conditions of concentrated solutions. With such dolomites 

 this paper is not directly concerned. In this communication 

 discussion will be limited to those " regional " cases of dolo- 

 mitization such as are represented by certain recent coral lime- 

 stones where no concentration of sea water or elevation of 

 temperature can be postulated. 



Extensive references to the literature of the subject will be' 

 found in the following papers : 



* J. D. Dana, Geology of United States Exploring Expedition, p. 153, 1849. 

 t J. W. Judd, The Atoll of Funafuti, London, pp. 362-389, 1904. 

 JE. W. Skeats, Monograph of Christinas Island, pp. 265-8, 1900; Bull. 

 Mus. Comp. Zool., Harvard, vol. xlii, 53-126, 1903. 

 § E. W. Skeats, op. cit. 

 || Idem, Q. J. G. S., lxi, 97-141, 1905. 



Am. Jour. Sci.— Fourth Series, Vol. XLV, No. 267.— March, 1918~ 

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