KEWEENAW FAULT 



95 



represent more nearly the geological structure. Figures 7 and 8 with 6 cor- 

 respond to 5. 



The Primitive Keweenaw Fault 



We 5 agree that the faulting began in Keweenaw time. In figure 2, by changes 

 from figure 1, I have tried to show (1) that J) of the Keweenawan lies on the 

 underlying Huronian unconformably, the beds in contact on the two sides 



Figure 2. — Ideal Sketch of the same Fault as Figure 1, supposing it to be a Block-fault 



differing many thousands of feet in horizon. This is well marked around 

 Sunday Lake, as noticed by H. L. Smyth, Rose, and others. In fact, according 

 to Allen's recent discoveries, the whole Upper Huronian was eroded away 

 along much of the Gogebic range. (2) That this fault-line acted as a channel 

 or conduit for volcanic activity, so that intrusive pipes (h) and sills (g) are 



Figure 3. — "Ideal Sketch of the Keweenaw Fault, after the Deposition of the Eastern 

 Sandstone and before the secondary faulting" 



As represented in figure 25, loc. cit. 



found near it — for example, Mount Bohemia gabbro, the Torch Lake quartz 

 porphyry, Indiana Mine porphyries and gabbro, Bergluud intrusives, etcetera — 

 and the more viscous felsic lavas are also found near it. One period of erup- 

 tion of rhyolites culminates before the deposition of conglomerate S, (c) of 



We" refers to the authors of Bulletin 23 and myself. 

 VIII — Bull. Geol. Soc. Am., Vol. 27, 1915 



