GEOLCXilCAL EXPLORATIONS AND LITERATURE. 39 



Sweet (E. T.). Notes on the Geology of Northern Wisconsin. Trans. Wis. 

 Acad, of Sci., Arts and Letters, vol. in, lS75-'76, pp. 40-55. 



This is an outline account of observations in northern Wisconsin made 

 in 1S73 and 1875 for the Wisconsin State Geological Survey. The quota- 

 tion below gives certain facts with regard to the Bad river and Penokee 

 gap section. It should be said that I afterwards measured this section in 

 detail for the Wisconsin Survey and the results were published in the third 

 volume of the Geology of Wisconsin. The thickness of the Iron-bearing 

 series is more than twice as great as supposed by Mr. Sweet, the uppermost 

 beds being far above the uppermost mentioned by him. Two magnetic 

 belts, moreover, do not exist, as supposed by Mr. Sweet, the supposed 

 two belts being the same belt faulted apart. 



The junction between the Laiirentian and Huronian i.s in the southern part of 

 Sec. 14, T. 44, E. 3 W. At this point Bad river passes through a narrow gorge 

 having nearly vertical walls on either side. In the left or northern wall of the gorge, 

 tine grained white ([uartz with a vitreous coating and slaty siliceous schist occur, 

 showing a strike nearly east and west, and dip of 66° to the north. The quartz 

 represents the lowest member of the Penokie system examined by the party iu 1S73. 

 Upon examining the opposite wall of the gorge siliceous marble was discovered for 

 the first time to be one of the beds of the Penokie system, lying below the iron-bear- 

 ing beds. A similar arrangement has long been known to exist iu the Huronian of 

 the Marquette district, which has led to the suspicion of its existence in Wiscon- 

 sin. The thickness of the siliceous marble is about 50 feet. It is usually fine 

 grained and grayish iu color. Small crystals of calcite and dolomite, however, can be 

 observed irregularly disseminated. An analysis of a specimen taken from the ledge 

 afl'orded me the following result : 



Per cent. 



Carbonate of lime 50'52 



Carbonate of magnesia 33-41 



Insoluble nuitter 13-85 



Oxide of iron 1-70 



Undetermined -52 



Total 100-00 



The analysis shows that the proper name for the rock is siliceous dolomitic mar- 

 ble. In the Martjuette region the Morgan furnace limestone, but very little piurer than 

 this, has been extensively used as a tiux. One huudred feet southeast from the expo- 

 sure of siliceous marble there is a large ledge of gneissoid granite showing a well 



