. Bulletin of the Geological Society of America. Geology. FIELD STUDIES OF CONCRETIONS IN SHALE 677 slipping off the steep sides of the concretion and accumulating around it (see figure 1). As burial proceeded, the normal bedding planes passed over the concretions and eventually all evidence of the concretion died out. A feature of considerable import noticed on these concretions was their marked slickensides. These were on both the under and upper sides, but were far less perfectly developed below. In the entire absence of evidence. Figure 1.—Sketch of Concretion in Pennsijlranian Shale in Bo
. Bulletin of the Geological Society of America. Geology. FIELD STUDIES OF CONCRETIONS IN SHALE 677 slipping off the steep sides of the concretion and accumulating around it (see figure 1). As burial proceeded, the normal bedding planes passed over the concretions and eventually all evidence of the concretion died out. A feature of considerable import noticed on these concretions was their marked slickensides. These were on both the under and upper sides, but were far less perfectly developed below. In the entire absence of evidence. Figure 1.—Sketch of Concretion in Pennsijlranian Shale in Boone County, Missouri Shows lenses of clay between the bedding planes. of lateral growth, such as crumpling of the beds, which would be neces- sary in these beds, because the concretion is not due to local cementation, as shown by the stratification planes passing over and not through them, it must be concluded that the slickensides are due to upward growth sub- sequent to deposition, or that the beds slipped down around the concretion during consolidation. CONCRETIONS IN THE CRETACEOUS (GRANEROS) SHALES IN SOUTH DAKOTA AND WTOMING The lower part of the Graneros shale (Cretaceous) in the northern Black Hills contains many concretions. Some of the best of these are in Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Geological Society of America. [New York : The Society]
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