192 F. W. SARDESON GALENA SERIES 



graphic scale and equal formational division. By determining first of 

 all the value of the units, which each author had recognized, these could 

 then be compared in terms of a uniform stratigraphic-paleontologic scale. 

 Besides the early reports of D. D. Owen, John Locke, J. G. Perceval, 

 I. A. Lapham, James Hall, J. D. Whitney, and C. A. White, the descrip- 

 tions by A. H. Worthen, H. C. Freeman, Frank H. Bradley, and James 

 Shaw in Illinois, by T. C. Chamberlin, R. D. Irving, and Moses Strong 

 in Wisconsin, by Chas. E. Keyes, W J McGee, Samuel Calvin, W. H. Nor- 

 ton, and others in Iowa, and by N. H. Winchell, C. W. Hall, E. 0. Ulrich, 

 and others in. Minnesota, could be cited so as to set a standard for uni- 

 formity in practically every part of the field. In a former publication* 

 I have offered such a comparison of the work of the authors named. Al- 

 though this was set forth, necessarily, in brief form, it was hoped that it 

 would serve to introduce a consistent use of formational units if per- 

 chance fellow-workers desired such to prevail. 



The Maquoketa series was included with the Galena series in that 

 effort, and in regard to the Maquoketa it may be noted that the calcareous 

 beds are no longer called Niagara in Minnesota,! the absence of Silurian 

 and the unconformability of the Devonian on the Ordovician being appar- 

 ently recognized there and in northern Iowa. J In Fayette county, Iowa, 

 also the calcareous Maquoketa beds are recognized as such and not called 

 Galena,§ as the same had been in the near-by county. In regard to the 

 Galena series, on the other hand, results are meager. Discussion and 

 description of the Galena series have been put forth from the point of 

 view of the lead and zinc region. The economic aspect of the subject due 

 to lead and zinc deposits, which seems earlier to have rather hindered a 

 careful correlation of strata between Beloit and Platteville, for example, 

 appears now to ignore even that geologic correlation which has been put 

 ready to hand. Since Van Hise|| has recognized certain important rela- 

 tions between ore deposits and organic matter in strata in the Galena 

 series, it may be essential that greater care in the marking of organic zones 

 should follow. The formational boundaries should accordingly be estab- 

 lished not by lithologic characters which may run obliquely across a par- 

 ticular organic zone, putting it into two such geologic formations, but by 

 such characters as may place a particular zone in uniform relation to one 

 formation in which it lies and to other such zones. 



* American Geologist, vol. xviii, 1896, p. 356. 



t Geological and Natural History Survey of Minnesota, vol. vi, 1901, preface plate. 



t Op. cit, description to plate 10 ; and Iowa Geological Survey, vol. 13, 1901, p. 39. 



§ Iowa Geological Survey, vol. ir>, 1905, pp. 438 and 463. 



II U. S. Geological Survey Monograph, vol. 47, 1904, p. 1157. 



