. Bulletin of the Geological Society of America. Geology. 96 PROCEEDINGS OF THE WASHINGTON MEETING this figure. (3) Therefore I have changed the hade of the fault from that of an overthrust to the steep hade of a block-fault. There is some direct evi- dence of this. It is certainly not as flat as a later overthrust fault (Old Colony and Torch Lake and Oneco sections). A nearly vertical hade would be also a more natural channel for volcanic activities. Many overthrust faults are devoid of them. Primitive Erosion We agree, as shown in figures 3 and 4, that this primitive fault suffered erosion,
. Bulletin of the Geological Society of America. Geology. 96 PROCEEDINGS OF THE WASHINGTON MEETING this figure. (3) Therefore I have changed the hade of the fault from that of an overthrust to the steep hade of a block-fault. There is some direct evi- dence of this. It is certainly not as flat as a later overthrust fault (Old Colony and Torch Lake and Oneco sections). A nearly vertical hade would be also a more natural channel for volcanic activities. Many overthrust faults are devoid of them. Primitive Erosion We agree, as shown in figures 3 and 4, that this primitive fault suffered erosion, and that the Eastern or Jacobsville sandstone may have lapped on both sides of it. But the study of land formations, which has much advanced in the last 20 years, would lead one to infer that the valley at d was being filled as it was formed, and that there is no such sharp gap in dip or strike or time of deposition between the Upper Keweenawan and the Cambrian sand- stone, as is fairly inferable from figure 3. Tn fact, my own figure 4 does not do justice to my conception of the continuity of sedimentation that takes. Figure 4.—A Stage corresponding to Figure 3 Showing the section after the deposition of the four Paleozoic overlaps place in a block-fault valley or graben. The Keweenawan is for me largely the land facies (the Old Red Sandstone facies) of the Middle and Early Cambrian (Waucobic). We know now definitely through Thwaites and the Wisconsin Survey that the Upper Keweenawan is indistinguishable in lithology, dip, or strike from the Cambrian sandstones, for the "Western" Apostle Islands sand- stones that have been hitherto called Cambrian by every one he classes as Upper Keweenawan, and the line between them and the Mississippi Valley fossiliferous Upper Cambrian sandstone is drawn in a region where there are no outcrops. However, Limestone Mountain at .;' has fortunately been left us (figure 8) to show that the "Eastern" sandstone is really direc
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