Back in my eastern Nevada field days, I was lucky enough to go on a stratigraphy tour that took me to several good examples of chert nodules in the mostly Pennsylvanian
Ely Limestone.
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| Nicely spherical chert nodules in the Ely Limestone, with 2.5 lb sledge for scale. |
In the 1950s and 1960s, R. A. Breitrick and J. E. Welsh described the detailed stratigraphy of the Ely Limestone in the area of Ely and the Robinson mining district (with Breitrick, at least, continuing to work in the area to this day). They divided the formation into mappable units, W through C,
bottom to top. (Their units A and B have since been placed in the overlying Permian
Riepe Spring Limestone.) The only summary of this stratigraphy I could find online is shown
here (pdf; Maher, 1995, p. 22).
Several units within the Ely, notably units S, R, P, L, and F, contain
cannonball cherts (although I'm not sure about the details of units T, U, V, and W: I can't find my field sheets in the mess my office is currently in!). Theses photos are most likely from S, R, or P (my thoughts).
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| Fairly large, sub-spherical chert nodule. |
This is the best example I have of a chert nodule that is approaching "cannonball" in size and shape. Apparently, cannonball chert nodules can weather out and end up looking a lot like loose cannonballs. An excellent example of a loose cannonball nodule can be seen
here [pdf] on page 27 (Maher, 1995, Fig. 7C).
These photos were taken in the spring of 2007 on the northeastern slopes of
Rib Hill, a location that might or might not be accessible from Highway 50 or Route 6 via a side road formerly known as S.R. 44 or
S.R. 485 (the location might be behind a locked gate).
