112 R. T. Hill — Hematite and Martite of Mexico. 



and diorite are crossed, all of which strike in the direction of 

 the axial trend of the mountain, with slight local sinuosities. 

 At an elevation of about 1000 feet above the railway which 

 skirts the base of the mountain, and nearly at the summit, the 

 original source of the iron debris of the plain is found in 

 large masses, or pseudo-veins, of ore, the bodies of which 

 occur in a line corresponding with the strike of the limestone 

 diorite contacts, and are principally exposed at the crests of 

 the ridges dividing the lateral canons. The ore bodies resem- 

 ble fragments of a vertical vein, but apparently have no direct 

 continuation. They occur along the line of contact between 

 the upper limestone and the diorite, but some of the masses 

 are entirely embedded in the limestone and others in the 

 diorite, while several present a wall of each. The bodies 

 could not be described as lenses, as are the masses of specular 

 ore in either Algonkian or Archaean schist in Llano county, 

 Texas, nor are they true beds, but apparently formed by the 

 replacement of the limestone at the liniestone-diorite contact, 

 or replacement of the masses of limestone included in the 

 diorite. The principal outcrops, seen along a north and south 

 line of six miles, were as follows, beginning at the south end 

 of the mountain : 



1. The first lateral ridge projecting from the east side of the 

 north end of the mountain is crossed by the vein or bed which 

 upon one side reveals a cross section of 30 feet and an expo 

 sure of 250 feet parallel to the mountain crest north and 

 south. 2. On the opposite side of the ridge apparently the 

 same bed reappears with a vertical exposure of 50 feet. 3. In 

 the same line of outcrop is a third exposure of apparently the 

 same mass as No. 1. 4. Northward are two outcrops with 

 areal exposures of 65x32 feet and 150x30 feet respectively. 

 5. One-half mile north of the above is another outcrop of the 

 ore with a surface area of 30X240 feet. 6 One quarter of a 

 mile northward is the mine known as La Paloma which has 

 been somewhat developed; it has an areal exposure of 45 X 

 200 feet and a vertical face of 50 feet. 7. Still northward is 

 an outcrop resembling No. 2 in quantity exposed. 8. Two 

 miles north and nearest to Monclova is the last outcrop visited ; 

 it has a vertical exposure of 150 feet and a width of 30 feet at 

 the top which rapidly diminishes downward. 



All of these masses, from their uniform width and con- 

 tinuity of strike are apparently genetically connected con- 

 tinuously along a structural parting between the diorite and 

 limestone. 



The ore presents peculiar mincralogical conditions. Where 

 the interior of the vein is exposed by blasting its mass con- 

 sists of a bright lustrous (specular) hematite. This would not 



