916 



SCIENCE. 



[N. S. Vol. XXIII. No. 598. 



tively barren and this variation in graphite 

 content is believed to express the original dif- 

 ference in percentage of carbon in the sedi- 

 ments. The graphite grains are minute and 

 intimately associated with muscovite and 

 quartz. The Madrid graphite is regarded as 

 the product of the conversion and concentra- 

 tion of carbonaceous particles of sedimentary 

 origin through the agency of heated vapors 

 from the pegmatite magma. 



In Yarmouth, the graphite is found within 

 a pegmatite dike which cuts a large granite 

 mass. The graphite in flakes and large masses 

 is a well-distributed constituent of the peg- 

 matite, and with the quartz and feldspar 

 forms the usual mosaic. No evidence was 

 noted of any source of the carbon of the 

 graphite other than in the molten rock which 

 intruded the granite itself, the graphite being 

 as much an essential and original constituent 

 of the pegmatite as is the quartz or the 

 feldspar. 



Copper Deposits of the Zuni Mountains, New 



Mexico: Mr. F. C. Schradeb. 



The Zuni Mountains form a group about 

 twenty miles long and fifty miles wide, situated 

 some eighty-five miles west of Albuquerque. 

 They are composed of pre-Cambrian schists, 

 gneisses and granites, and are flanked on all 

 sides by gently upturned strata regarded as 

 of upper Carboniferous age — the ' red beds ' 

 of the Colorado Plateau region. Mount 

 Sedgewick, the highest summit of the group, 

 rising 2,000 feet above the surrounding pla- 

 teau, reaches an elevation of 9,200 feet. The 

 topography is for the most part not rugged 

 and nearly every portion of the district may be 

 reached by wagons. The drainage goes to the 

 Eio Grande by way of the Blue Water and 

 San Jose rivers on the north, and the Agua 

 Fria on the south. The trend of the moun- 

 tains and of the dominant structure in the pre- 

 Cambrian rocks is a little north of west, and 

 the foliation of the schists and gneisses dips 

 steeply toward the south. 



Copperton, the principal mining camp, is 

 situated in the heart of the mountains about 

 twenty miles west of the Atlantic and Paciflc 

 Trans-Continental Eailway. 



Copper deposits are found both in the pre- 

 Cambrian rocks and in the lower strata of the 

 ' red beds.' In both situations the ores thus 

 far revealed consist almost entirely of second- 

 ary copper minerals including green and blue 

 carbonates and copper glance. Chalcopyrite, 

 though present, is uncommon. 



In the Pre-Cambrian the ores occur along 

 sheeted zones in the schists or gneisses, some- 

 times associated with quartz in irregular vein- 

 like bodies, but to a greater extent dissemi- 

 nated through the rocks of the mineralized 

 zones. These zones vary in width, the widest 

 observed being 800 feet across. They are 

 often persistent for considerable distances, and 

 in several instances the presence of workable 

 amounts of rock carrying above three per cent, 

 metallic copper has been demonstrated. The 

 \isual minerals associated with these ores are 

 quartz, specular iron, limonite, galena, and 

 pyrite. Gold values are said to run from one 

 dollar to four dollars per ton. 



The basal strata of the ' red beds ' which 

 carry copper minerals are from thirty to sixty 

 feet in thickness. At the bottom is an arkose 

 conglomerate and above this there are layers 

 of sandstone and shale. In the northwest 

 part of the district the conglomerate may be 

 seen resting upon the basset edges of the crys- 

 talline pre-Cambrian rocks. The ore minerals 

 are locally disseminated through the rocks, and 

 where occurring in the conglomerate appear 

 to have been deposited with the sand and 

 gravel which compose the rock. If this sug- 

 gestion is correct, the copper minerals were 

 probably derived by erosion from the pre- 

 existing deposits in the crystalline forma- 

 tions. The ore-bearing strata, and especially 

 the shaly beds, contain considerable amounts 

 of fossil wood, and this material has been 

 very largely replaced by copper carbonates and 

 glance, and cuprefacts produced in this way 

 form an important portion of the ' red bed ' 

 ores. 



The district has been under development for 

 about five years, but as yet there are no ship- 

 ping mines. Annual assessment work is done 

 on some 200 claims controlled by about Y5 in- 

 dividuals. The region is well watered and 

 forested, and the climate is a pleasant one. 



