482 E. STEIDTMANN ORIGIN OF DOLO^LITE 



Page 



Conditions of dolomitization in the sea 445 



Critical state between limestone and dolomite deposition 445. 



I )eptli of water 44(3 



Temperature of water 446 



Composition of sea-water 446 



Summary 447 



Marine or post-marine origin <>f dolomite 447 



Manner of marine dolomitization 448 



Condition of marine dolomitization 449 



Intkoductiox 

 the bases for inferences 



Direct observations ou the process of dolomitizatiou are all but lacking. 

 Its limiting conditions have not been found by experiments. Field and 

 petrographic facts, therefore, are at present the best bases from which 

 inferences as to its nature ma}- be attempted. 



Thus far most studies on the origin of dolomite have been based on 

 (1) published field and petrographic facts of a general nature which were 

 not collected with the specific aim of throwing light on the dolomite 

 question, and (2) generalizations which grew out of the general field and 

 petrographic facts just alluded to. To this type of inquiry into the origin 

 of dolomite the waiter- contributed in 1911. He is now convinced that 

 progress on the dolomite prol)]em will be made chiefly Ijy direct studies 

 of dolomites themselves. This paper jDresents the principal results of his 

 first attempt by the direct method. 



A perplexing difficulty involved in the method of direct attack is to 

 know what to look for in dolomites and to know how to e\'aluate the 

 bearing of observed facts on the question of dolomite genesis. Tliis diffi- 

 culty will no doubt be less felt when more direct studies like those of 

 Skeats and others have been inade. Even now the application of the 

 direct method promises great rewards. 



AIM AND METHOD OF STUDY 



This paper aims to present a feAv direct observations on dolomites and 

 their bearing on the time, manner, and conditions of dolomitization. It 

 is based on a study of specimens and slides in the collections at the Uni- 

 versity of Wisconsin, but mainly on studies of the Paleozoic rocks of Wis- 

 consin. The writer is indebted to W. 0. Hotchkiss, State Geologist of 



- K. Steifltmann : KAolvitjon ot limcf^lono !\^(] Oolorajlc, .Toiiv. of Ceo],. 1911. 



