lEONOKE DEPOSITS OF NEGAUXEE FOliMATlON. 395 



area. The best examples of these de})Osits are those occurring iit the Teal 

 Lake range anil east of Negaunee (Atlas Sheets XXVII and XXXI). 

 Here are situated the Cleveland Hematite, the Cambria, the Bufialo, the 

 Blue, and other mines. These ore deposits have as their foot-wall the 

 Siamo slate. A striking fact about these deposits is that all of those 

 mentioned, and all of those known, occur at places where the Siamo 

 slate is folded so as to form a trough. By reference to the maps (Atlas 

 Sheets IV and XXVII) it is seen that all the Teal Lake mines occupy a 

 place where the iron formation curves to the north and then swings back to 

 its original course, the ore deposits thus resting upon a southward-pitching 

 trough of the slate. Still more striking is the occurrence east of Negaunee. 

 Here the ore bodies occur at places where the slate is folded so as to 

 furnish sharply pitching synclinal troughs, which plunge to the west. 

 (PI. XXIX, figs. 3 and 4.) It is further found, by an examination of the 

 workings, that the iron-l^earing formation is often cut by a set of steep or 

 vertical dikes, and that the conjunction of these dikes with the foot-wall slate 

 forms sharp V-shaped troughs. This is particularly clear in the case of the 

 Cleveland Hematite mine, where, between a series of vertical dikes and the 

 Siamo slate, the ore bodies are found. By comparing this occurrence with 

 the ore deposits of the Penokee range, ^ it will be seen that they are almost 

 identical, in each case there being on one side of the formation an imper- 

 vious slate and quartzite, and upon the other an impervious dike, the two 

 vmiting to form a pitching trough. 



(2) The typical area for the soft-ore bodies within the iron formation 

 is that of Ishpeming and Negaunee. Here belonging are such deposits as 

 the Cleveland Lake, the Lake Angeline, the Lake Superior Hematite, the 

 Salisbury, and many others. When these deposits are examined in detail 

 it is found that the large deposits always rest upon a pitching trough com- 

 posed wholly of a single mass of greenstone (PI. XXVIII, figs. 4-6), or on 

 a pitching trough one side of which is a mass of greenstone and the other 

 side of which is a dike joining the greenstone mass. The underlying rock is 

 called greenstone, although immediately in contact with the ore it is known 

 as paint-rock or soapstone by the miners. 



'The Penokee iron-bearing series of Michigan and Wisconsin, by R. D. Irving and C. R. Van 

 Hise: Mon. U. S. Geol. Survey, Vol. XIX, 1892, pp. 268-294. 



