958 



SCIENCE 



[N. 8. Vol. XXVII. No. 703 



rado Eiver and between the river and the Colo- 

 rado Plateau. They represent the southward 

 continuation of the Virgin and Muddy Moun- 

 tains of the Great Basin on the north. The 

 principal distributing point for the mining 

 districts is Kingman, situated on the main 

 line of the Atchison, Topeka and Santa Fe 

 Eailway. 



The deposits, concerning which little has 

 hitherto been known, occur principally in two 

 regions: One in the Cerbat Moimtains, where 

 the deposits are distributed over an area that 

 extends from about nine miles north of King- 

 man to twenty miles north, embraces the 

 Chloride, Mineral Park, Stockton Hill and 

 Cerbat districts. The other region is in the 

 southern part of the Black Mountains, where 

 it embraces the well-known Gold Eoad and 

 Vivian districts, situated about twenty-four 

 miles southwest of Kingman. Both regions 

 contain numerous mines, many of which have 

 produced from about $1,000,000 to $3,000,000 

 each; the production of the Gold Eoad mine 

 being about $1,000,000 in the two years 1905 

 and 1906. 



The deposits are of two very distinct types. 

 The first, which is confined chiefly to the 

 Cerbat Eange, consists of quartz fissure veins, 

 usually in the pre-Cambrian complex of 

 granitoid-gneiss-schist rocks. The veins usu- 

 ally are not deeply oxidized. They contain 

 the sulphides, pyrite, galena, zinc blende and 

 arseno-pyrite, which yield silver chiefly, but 

 with minor amounts of gold. 



The second group comprises the deposits of 

 the Black Mountains. They differ markedly 

 from those of the Cerbat Eange, just de- 

 scribed, in several important respects. First, 

 they oec.ur chiefly in Tertiary volcanic rocks, 

 principally andesite, and are younger than 

 the Cerbat veins. Second, the veins seem to 

 have originally contained a calcite gangue, 

 which is still present in many of them. In 

 the most valuable deposits, however, a min- 

 eralogical change has taken place, by which 

 the calcite has been replaced by quartz and 

 adularia. Third, the values are almost exclu- 

 sively gold. Fourth, the oxidation extends to 

 the depth of 600 or 700 feet, and, as a rule, 

 no sulphides or base metals are found. 



The deposits of both types are believed to 

 owe their origin to the circulation of min- 

 eralized, aqueous solutions probably at high 

 temperatures through the fissures in which the 

 values are now found. 



Recent Work on the Illinois Coal Field: Mr. 



Frank W. De Wolf. 



The Illinois Coal Field covers an area ex- 

 ceeding 36,000 square miles and supports over 

 four hundred commercial mines scattered 

 through fifty counties. The preliminary esti- 

 mates place the production for 1907 in excess 

 of forty-nine million tons, and thus indicate 

 an increase during the year of over twenty 

 per cent. 



While the general features of the stratig- 

 raphy and structure have been presented in 

 earlier reports, the problem remains to divide 

 the stratigraphic column into appropriate 

 formations and to carry the correlation of the 

 sixteen or more coals through the state. This 

 work is going forward by cooperative investi- 

 gations of the State and U. S. Geological 

 Surveys. 



Certain chemical problems have been in- 

 vestigated, also; one refers to variations in 

 the quality of coal seams from place to place; 

 another, to the relation between analyses of 

 mine samples and commercial samples, with 

 especial regard to the deterioration of coal 

 during storage. Another consideration of 

 vital importance refers to the selection of 

 some " pure coal " unit which may serve as a 

 basis for comparing samples of varying com- 

 position. 



Detailed reports are finished for parts of 

 Saline, Gallatin and Williamson Counties. 

 The explored rocks include some fifteen hun- 

 dred feet of carboniferous sediments, and 

 these include two widely persistent coals of 

 approximately five feet in thickness and of 

 excellent quality, besides numerous local beds. 

 The dip of the rocks is essentially northward 

 toward the center of the basin, but is inter- 

 rupted locally by dome-like features which 

 suggest block-faulting on a small scale. The 

 structural relief, as shown, is four hundred 

 and twenty-five feet. In some cases the coals 

 are cut by igneous dikes which produce nat- 



