EVIDENCE OF THE MIDDLE-UPPER HURONIAN 



UNCONFORMITY IN THE QUARTZITE HILLS 



AT LITTLE LAKE, MICHIGAN 



R. C. ALLEN AND L. P. BARRETT 



A critical examination of the exposures of quartzite, quartz 

 slate, and arkose in the hills near Little Lake in T. 45 N., R. 24 W., 

 Marquette County, Michigan, was inspired by the results of recent 

 studies by the senior writer in the Gwinn synclinorium, which lies 

 between five and seven miles west. 



The Gwinn synclinorium contains two series of Huronian 

 sedimentary rocks, separated by an unconformity which is charac- 

 terized by a conglomerate at the base of the upper (Princeton) 

 series containing fragments derived from the various formations 

 (including a productive iron-bearing member) of the lower (Gwinn) 

 series and also from a third sedimentary series not represented in 

 the synclinorium. The work at Little Lake resulted in the identi- 

 fication of an unconformity which, in connection with other data 

 to be described, establishes a basis for correlation of the formations 

 at Little Lake with certain of those in the Gwinn synclinorium. 



So far as the writers are aware, no previous mapping and care- 

 ful study of the rocks at Little Lake has been made. Rominger 

 barely mentions the locality in 1894 in the statement that "iron- 

 bearing rock beds occur in the vicinity of Little Lake.'"^ Reference 

 was again made to this locality in 191 1 by Van Hise and Leith^ 

 who correlated the quartzite, quartz slate and arkose in the hills 

 at Little Lake with the Goodrich quartzite or basal member of the 

 Upper Huronian as developed in the Marquette district and the 

 arkose and arkose conglomerate at the base of the Gwinn series 

 in the adjacent Gwinn (Swanzy) synclinorium. 



The succession and correlation of the formations in the Gwinn 

 synclinorium and those at Little Lake are given below: 



^Michigan Geological Survey, 1894, Vol. V, Part I, p. 71. 

 ^ C. R. Van Hise and C. K. Leith, Monograph 52, U. S. G. S., pp. 2S3-86. 



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