. [Reports]. Terre are located andin the other the Flat River Mines. In other words a ridge of sand-stone separates the ore horizon of the St. Joseph Lead Companysmines at Bonne Terre from the ore horizon of the mines locatedsouth of Big River. This ridge of sandstone is buried beneath theBonneterre dolomite which gradually diminishes in thickness to-ward the east and increases in thickness toward the west. Theridge appears to flatten out and disappears about three miles north-west of Desloge. BONNETERRE FORMATION. The Lamotte sandstone is overlain with the Bonneterre forma-tion which has a no
. [Reports]. Terre are located andin the other the Flat River Mines. In other words a ridge of sand-stone separates the ore horizon of the St. Joseph Lead Companysmines at Bonne Terre from the ore horizon of the mines locatedsouth of Big River. This ridge of sandstone is buried beneath theBonneterre dolomite which gradually diminishes in thickness to-ward the east and increases in thickness toward the west. Theridge appears to flatten out and disappears about three miles north-west of Desloge. BONNETERRE FORMATION. The Lamotte sandstone is overlain with the Bonneterre forma-tion which has a normal thickness of approximately 363 feet ofdolomite, arenaceous, chloritic and argillaceous in the lower por-tion and slightly argillaceous near the top. The Bonneterre for- *The beds here called dolomite are magnesian limestone in which the percentages of magnesiumand calcium are variable. However, they have all the usual characteristics of dolomite and aretherefore called by this name in the present BONNETERRE FORMATION. 27 mation varies considerably in thickness, since it overlaps the La-motte sandstone and over-rides its billowy surface. The greatestthickness of which I have a record is for a drill hole near Delassuswhich passes through 448 feet of dolomite before penetrating thesandstone. Other records in the neighborhood of this hole showthicknesses of 440 and 435 feet. Southwest of Elvins in Sec. 22,T. 36, R. 4E., the* thickness varies somewhat, the maximum re-corded being 355 feet. In Sec. 12, T. 36, R. 5E., the thicknessvaries from 396 to 406 feet. West of Irondale a maximum thick-ness of 310 feet has been recorded. On the land grant, U. S. Sur-vey 3063, north of Farmington Junction there are several holeswhich indicate a thickness of about 380 feet. In the vicinity ofBonneterre this dolomite is about 400 to 440 feet in thickness asshown by numerous drill holes. West of the city of Bonne Terreon Sees. 2, 10 and 11, T. 37, R. 4E., drill holes show a thickness o
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