60 YEARBOOK, PUBLIC MUSEUM, MILWAUKEE. [Vol. I. 



never been satisfactorily explained. These domes of salt are deeply 

 buried beneath sand and gravel ; a low broad mound on the surface re- 

 flecting the presence of the dome beneath. Several hundreds of these 

 domes have been discovered in the region between the mouth of the 

 Mississippi and that of the Rio Grande and nearly all have been pene- 

 trated by the drill and found to contain commercial deposits of one kind 

 or another. So far three valuable minerals have been found to be pres- 

 ent in these domes: salt, oil, and sulphur. The central core of each is 

 composed of salt and. in many, the upturning of the rocks has allowed 

 great quantities of petroleum to accumulate. Only three, however, have 

 been found to contain sulphur and in each case this occurs in limestone 

 associated with the mineral, gypsum. 



The original discovery of sulphur in these domes occurred at Sulphur 

 Mound, St. Charles Parish, Louisiana, and efiforts were immediately 

 made to sink a shaft to the deposit and commence mining. These failed 

 because of the difficulty of maintaining an open shaft through so great 

 a thickness of unconsolidated sand and gravel and the project was at 

 length abandoned. However, a chemical engineer, who had been em- 

 ployed ])y the original company continued experiments and at length 

 perfected a process called after him, the Fraasch process, by which the 

 ore below could be extracted. Since that date, the production of the 

 sulphur from these mounds has been continuous and so large an amount 

 of the mineral has been obtained that the supply is sufficient to meet the 

 demand of the sulphur users of this country and still leave a large mar- 

 gin for export. 



In brief, this method consists of melting the sulphur underground 

 by means of superhea'ed steam and removing it to the surface, where 

 it cools and crystallizes. This latter is accomplished by the pressure of 

 air pumped down the well. This method has the great advantage of 

 yielding a product which is practically pure and needs no further re- 

 fining before being put upon the market. Simple in its theory ; never- 

 theless, successful operation involves the overcoming of a large number 

 of mechanical difficulties. 



The sulphur deposits at Freeport underlie a mound approximately 

 twenty-five feet in height and covering an area of five hundred and 

 thirty acres. The removal of the sulphur has caused the mound to dis- 

 appear and the site is now marked by a slight depression. The dome 

 beneath rises to within approximately nine hundred feet of the surface, 

 and is buried beneath sand and gravel. The capping rock is limestone 

 and appears to be broken into huge blocks probably by the force of the 



