No Limestone for You, TLRC! (part 2)

Avid readers of the blog will recall that The Logging Road Cyclist was nearly delirious with joy at the prospect that he finally might have discovered, high up on Laurel Mountain, an outcrop of the long sought after Rickreall Limestone Member of the Yamhill Formation  (cf. Laurel Mountain Plateau).

Reader commentary was clamorous, uniformly positive and evenly divided into the “Way to go TLRC! We knew you’d do it!” and the “Thank god, we don’t have to listen to that anymore!” camps.

But TLRC, with scientific rigor drilled into him by 30+ years of trying to avoid research errors, remained skeptical. After all, the early published reports on the Limestone made it clear that it is comprised mainly of the shells of tiny little critters, which his rock might or might not have been (no paleontologist, TLRC). Limestone should fizz when doused in acid; vinegar left the rock dormant. Perhaps, TLRC thought, he needed stronger acid. More likely a stronger mind. Thus, rock in hand, TLRC found himself at the door of the kind and patient Professor D., Ph.D., at OSU.

As Prof. D. looked over the find TLRC was pleased that he (PD) didn’t immediately ID the rock. TLRC was prepared for a jaunty ” For the love of god, TLRC, this isn’t limestone. Where did you go to school, anyway?” Rather, TLRC encountered Modern Geology, which impressed him no end. After a couple of informed speculations (and some stronger acid) , PD simply said “I don’t know, want me to X-ray it and see?” Cutting to the chase, indeed. Here was a man after the efficient heart of TLRC!

Within 48 hours, back came the results:


Here is the XRD pattern.  Looks like albite (sodic plagioclase) and quartz…might be a bit of K-feldspar/orthoclase….. so kaolinite and reddish earth hematite are minor.  My guess is that this is a tuff or more likely a tuffaceous sandstone (lacking much ash) that has had ash removed by water transport.  Pretty interesting, because it must represent a relatively silicic volcanic eruption somewhere nearby.

It should be noted that this was, in fact one of the informed speculations prior to analysis.

TLRC’s NiteRiding buddy, Professor H., Ph.D., MMQ (Monday Morning Quarterback), who, through his Network, was apprised of the results even before TLRC, sent TLRC a rather arch text message in which he (PH) informed TLRC that his guess, pre-analysis, tallied more or less exactly with the results. To which TLRC offers up a huh.

All this sent TLRC back to the literature. What could this be? He had never heard of this sort of thing in the Coast Range. Thus is displayed the silence of ignorance. Three or four minutes with the Google turned up the classic 1948 study of Snavely and Baldwin, “Siletz River Volcanic Series” (AAPG Bulletin, 32, 5, pp 805-812)  in which they note: “The interbedded sedimenatry rocks are predominant water-laid tuff and tuffaceous siltstone and sandstone ….”, so it really shouldn’t have been a surprise.

The writing on the wall is clear. More riding and nosing around accompanied by more study… woe is the readership.




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