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MAy, 1904. GEOLOGY OF WESTERN MEXICO—FARRINGTON. 211 
ported analyses of the ore by the latter show no Fe O, an omission 
which has been remarked by Cohen.* ; 
Rangel, however, states that true magnetite does not exist 
upon the mountain, except as its presence is indicated in small quan- 
tity by a feeble magnetism exhibited by some specimens.7 
The present writer failed to find any typical magnetite on the 
mountain, although a black powder occurring on the northern side 
proved to be slightly magnetic. Moreover, in carrying a compass 
needle over the mountain no deflection was noticed at any point. 
Witherbee states, however, that recent surveys show needle 
variations of from one to ten degrees.i Regarding the occurrence of 
magnetite he states in the same article, that while he once ‘‘went 
on record to the effect that ‘there was not a cart-load of magnetite 
on the mountain,’”’ he is now of the opinion that there may be some 
magnetite there. This opinion is based on the needle variations 
above mentioned, and by magnetic grains found among the anthills. 
Further, of numerous samples ground up for analyses, while some 
Were non-magnetic, others could be separated into a magnetic and 
non-magnetic part. Moreover, lodestone has been found at a locality 
‘west of “the cross.”’ 
Tt seems evident, from the above considerations, that on the 
whole the ore of the Cerro Mercado may be regarded as chiefly hema- 
tite, although in many cases doubtless, a mechanical mixture of 
magnetite occurs. | 
This hematite varies considerably in physical characters, being 
now hard-and now soft, now black and now red, now specular and 
now earthy. Of these varieties, the hard, solid, black ore is the 
most abundant and forms the chief mass of the mountain. It is 
this which forms the prominent cliffs and columns and projecting 
spurs. It is essentially solid and continuous, although narrow 
open spaces frequently penetrate it, usually lined with octahedral 
crystals of martite. The hardness and toughness of this ore are 
such as to make the task of mining and crushing it a difficult one. 
It is very severe, Witherbee states, on the hard parts of crushers, 
and will cut into the face of the hardest steel hammers. In fact, 
this toughness has been a serious obstacle hitherto to the use of 
the ore, and has resulted in the utilization chiefly, up to the present 
time, of the soft red variety found at the base of the mountain. 
Many analyses of the ore have been made and are quoted by 
*Zs. Kryst., Vol. 3, p. 632. 
TBol. Inst. Geol. de Mexico, Num. 16, p. 6. 
}Mining World, March 12, 1904. 

