Geography and distinctive characters. The fluorspar, lead, and zinc deposits that were the subject of the investigations reported in this paper are situated hi Livings ton, Crittenden, and Caldwell, and adjacent portions of Christian, Trigg, and Lyon counties, in western Kentucky, and in the counties immediately across the Ohio River, in the extreme southern portion of Illinois. This area, constituting what may be aptly termed the Kentucky-Illinois fluorite district, contains also lead, zinc, and other minerals in subordinate quantities and values. It is usually considered a minor division of the lead and zinc districts of the Mississippi Valley, but is in some ways rather sharply distinguished from the other districts of the valley. It differs from the other districts chiefly in the following respects: (1) In the presence of basic igneous dikes; (2) in the abundance of fluorite and its almost constant association with the lead and zinc ores; and (3) in the mode of occurrence of the ores, which are found principally in true fissure .veins that have resulted from fracturing and subsequent faulting. In the other districts the lead and zinc are of primary importance, while in this region the igneous dikes and the fluorite are the primary or predominant features and the lead and zinc are only incidental.
