The fissure system of El Potosi Mine of El Potosi Mining Company, Santa Eulalia, Chihuahua, Mexico

The fissures traversing the country were the means of mineralizing the district. The North-South system of fissures have been determined to be pre-mineral, hence the most important. Their intersections with cross fissures are the regions of orebodies, and the intersections have always produced ore of mineable quantity. Especially important are the intersections of fissures in the favorable (fossiliferous) limestone beds. The favorable limestones are easily recognizable and can be traced thru all parts of the district because of their distinctiveness and the uniformity of the structure of the region --Summary, page 19