504 University Geological Su.vey of Kansas. 
of deposition. Dolomite was formed before, during and 
after the formation of galena and sphalerite. Sometimes, 
however, it is of much later origin, as one specimen from 
Granby—a corroded galena crystal coated with a crystalline 
deposit of dolomite—shows. In most cases galena has pre- 
ceded sphalerite, but there are evidently two generations of 
galena, for the small octahedrons or cubo-octahedrons are 
almost invariably found on the sphalerite, and represent the 
second generation, while the cube or cubes slightly modified 
by the octahedron represent the first generation, being formed 
before the sphalerite. ‘There are also two or more generations 
of sphalerite, the second one appearing as small, reddish 
crystals in cavities. Pyrite is apparently in almost all cases 
formed after marcasite, while chalcopyrite precedes them 
both. Barite is usually found upon the calcite, but this is 
not always the case. 
Table III is a comparison of the minerals from the three 
most prominent lead and zinc districts of the Mississippi 
valley: (1) The Joplin district, of southwestern Missouri and 
southeastern Kansas; (2) the northern Arkansas district ; 
and (3) the upper Mississippi district, of Wisconsin, Illinois, 
and Iowa. Thedata for the northern Arkansas district were 
found in the Arkansas Geological Survey’s Annual Report for 
1892, vol. V, p. 251 et seq., by Branner; and that for the 
upper Mississippi in Geology of Wisconsin, vol. II, p. 691 et 
seq., 1871, by Strong; Geology of Wisconsin, vol. IV, p. 380 
et seq., by Chamberlain ; Lowa Geological Survey, vol. VI, p. 
25 et seq., 1896, by Leonard ; Iowa Geological Survey, vol. X, 
p. 498 et seg., 1899, by Calvin and Bain, 
