KEWEENAW FAULT 99 



wanted, however, to indicate, the still greater expansion and greater distance 

 from shoreline of the succeeding limestones. 



During the Paleozoic we have no evidences of great disturbances ; but four 

 times, as Case and Robinson show, the sea advanced over the region, quite 

 possibly when at periods of world-wide quiescence and peneplanation the 

 oceans were so filled as to raise the sealevels at about the same time when, as 

 four chief salients in Schuchert's curve indicate, there was wide-spread sub- 

 mergence of the North American continent. No unconformity and but little 

 disconformity has yet been recognized in these strata in Michigan. They are 

 indicated in figure 4 as practically conformable except near where Limestone 

 Mountain was to be. I have indicated the Richmond as a mere filled channel 

 in the Trenton, because it seems to have been less widely distributed in 

 Michigan. 



There may well have been, we should expect that there were, later Car- 

 boniferous invasions, all traces of which have been removed. There is little 

 Devonian left. 



We have then : 



1. "Trenton" — Ordovician — Decorah — Black River : T. 



2. Cincinnatian R. 



3. "Niagara" — Upper Silurian — Lockport N. 



4. Mid-Devonian — probably Hamilton — compare the overlap at Milwaukee, 



Wisconsin D. 



The first and third I had recognized years ago ; the second and fourth Rob- 

 inson has just recognized. 



The Appalachian Revolution 



Home time after the Mid-Devonian the faulting, folding, and disturbances 

 of the "Eastern" sandstone took place, which on the whole are very slight, 

 but which left us Limestone Mountain (./') as a fortunate remnant. I take it 

 that the further disturbances along the Keweenaw fault, illustrated by figure 

 ">. from Irving and Chamberlin, and 6 and 7, were at about the same time. 

 They were certainly later than the deposition of the Eastern sandstone, and 

 had there been much disturbance earlier than the Devonian I think it would 

 have been registered at Limestone Mountain. Moreover, the earlier Paleozoic 

 is generally quiescent in the Great Lakes region; but the Appalachian Revo- 

 lution may well have had some effect even here. T have indicated this effect 

 in two stages. In figure 6. I suppose, a continuation of the block-faulting. 

 This is indicated by flatter dips, and even sometimes southerly dips, near the 

 fault along the range (New Baltic and South Lake mines). Though such 

 southerly dips may lie produced by simple thrust, it is easier at least to draw 

 them by supposing a monoclinic fold or faulting, such as shown, to precede 

 the thrust. Moreover, the consolidation of the beds i-d with a greater thick- 

 ness down to the Archean than on the side of h would naturally lead to some 

 folding or slump faulting on that side. Either with or without this prelimi- 

 nary bending it is easy to see that the same tangential compression that has 

 bowed Lake Superior and produced the thrust-faulting and folding described 

 by Thwaites, striking on an uneven wall, with soft sandstone on one side and 



