ORE DEPOSITION. 227 
This table was primarily worked out with the idea that some definite 
order in the deposition of different minerals at different depths might be 
found, but the writer is unable to see any definite law. he table is valu- 
able, however, for showing the average composition of the ores as derived 
trom the tests of many hundreds of thousands of tons. 
PARAGENESIS OF VEIN MATERIALS. 
Microscopic examination shows that while the dolomite of the earlier 
period existed before the mineralization, yet among the vein materials 
ferriferous dolomite, quartz, and barite have ordinarily crystallized simul- 
taneously. These minerals form large idiomorphic crystals, which are 
_ intergrown. Some of the sulphides seem to have been deposited at the 
same time with these gangue minerals, as is the case where crystals of 
pyrite are found interbedded in small dolomized areas which are surrounded 
by pure limestone, free from both magnesia and iron. 
In perhaps the majority of cases, however, the sulphides seem to have 
crystallized at a very slightly later period than the barite. While the 
barite generally accompanies the ore, its presence is no indication of more 
valuable minerals, for many large and solid barite veins are found which 
are practically barren. This is the case, for example, with the large barite 
vein at the end of Yopsie tunnel. In Tourtelotte Park and in Smuggler 
Mountain, especially in the Mineral Farm mine, there are great masses of 
barite which contain very little valuable ore. Under the microscope the 
rich polybasite ore of the Mollie Gibson is seen to be composed partly of 
barite in interlocking, tubular crystals, among which are scattered bunches 
of polybasite, which are irregular in shape and have no suggestion of 
crystalline form. The polybasite does not follow definite zones, but is 
deposited between and around the barite crystals, showing that it erystal- 
lized at a slightly later period than did the barite. On Smuggler Mountain 
one of the chief ores is the so-called ‘“ crisscross spar,” which is a barite in 
which is deposited tetrahedrite or tennantite in narrow seams. ‘These seams 
are usually nonpersistent, and typically they form small isolated crosses, 
which give the ore its name. The arms of the crosses have the appearance 
of belonging to definite fracture systems, which have traversed the barite 
in directions independent of the planes of crystallization and cleavage, and 
therefore have opened at a period subsequent to the formation of the 
