448 E. STEIDTM ANN- -(MJKilX Ol' DOI.OMnM-: 



The latter are reeoiinized by tJieJr relaiioii to fissures, I'Mults, and other 

 seeoiidary o]jeiiirigs. 



Direct ohservatioiis by the writer and publisbed facts showing that tlie 

 majority of dolomites arc marine in origin were cited. The direct obser- 

 vations reported were as follows: 



1. l^ure dolomites and limestones, as shown hy staining and analyses, 

 are far more abmidant than mixed Ijeds of limestone and dolomite. 



2. The occurrence of calcific casts in dolomite or of hollow casts 

 bounded by perfect molds indicates that the casts were deposited in dolo- 

 mite. 



3. 8ome dolomite rhombs are imbedded in a hornlike invpervious mass 

 of tine-grained marine calcite. They evidently were formed in the ooze 

 contemporaneously A^ith the calcite. 



The 2)ublished facts wliicli were set forth in support of the conclusion 

 that most dolomites were developed in the sea are : 



1. The distributio]) of most dolomites is I'elated to stratigrapliic planes 

 and not to fissures, faults, etcetera. Mixtures of dolomite and limestone 

 within a single l)ed, as a rule, are also sedimeiitary in origin, since they 

 are not related to secondary 0})enings. 



2. Limestone and dolomite formations frecfueutly alternate. 



• .'). Dolomitization generally shows no relation to the present pore space 

 of beds. 



4. The abundance of botJi limestones and dolomites in the strata of 

 all ages does not fit the \'iew tliat dolomites are wholly the metasomatic 

 ]jroducts of underground waters. Tlieir time relatiojis seem to have re- 

 sulted from oscillations in marine conditions of deposition, 



5. Artificial replacements of calcite and aragonite by dolomite have 

 Ijeen etfected ])y soluti(Mts comparable to sea-waters, but not by carbonated 

 waters similar to the a\erage underground waters. 



G. Many (-oral islands of tlie l*acific are dolomitized. Sea-waters alone 

 could ha ^'e been responsible J'or this change. 



21A^yF,U OF MARINF DOLOMITIZATION 



Marine dolomitization inay lia\e l^een accomplished by direct precipi- 

 tation and l)y reactions within the sediments of tlie seadjottom, such as 

 rei)lacement of linn^ carbonate, recrystallization of MgO-bearing lime 

 carboiuite skeletons, and crystallization of dolomite from sea-waters in 

 the ooze. 



The results of staining show tliat the replacement of lime carbonate is 

 an important process. Replacement is pro\'en by the bunchy, irregular 

 distribution of dolomite grains witli respect to the bedding in mixed beds 



