Newcomb's Folly

Nearly all clastic dikes in the Channeled Scablands are Pleistocene in age, wedge-shaped, and filled from above (Jenkins, 1925; Lupher, 1944; Black, 1979; Woodward-Clyde, 1981; Pogue, 1998; Cooley, 2020). Upward tapering clastic dikes are very rare - one in one thousand at most. The dikes' wedge-shaped geometry, plainly observable in roadside exposures throughout Eastern Washington, has for far too long remained unclear. In this post, I trace the mistake back to its origin, a 1962 abstract by USGS geologist R.C. Newcomb. Let's revisit Newcomb's Folly.

Field geology still works. Geologist Olaf P. Jenkins examines a typical sheeted clastic dike in the Walla Walla Valley c. 1923. Jenkins published the first article on the clastic dikes of Eastern Washington (Jenkins, 1925) and Lupher (1944) the second. Both of which Newcomb ignored. Washington Geological Survey photo archive.

Newcomb's Folly - a misinterpretation of the dikes as upward-intruding structures - occurred in a 1962 abstract in the Newsletter of the Geological Society of the Oregon Country (GSOC). Reuben Clair Newcomb was a hydrogeologist for the U.S. Geological Survey tasked throughout the 1950-60s with refining the stratigraphy of Miocene to Quaternary sediments that lay beneath the Hanford Nuclear Reservation. Despite his years of service and a stack of formal reports to his name, one gets the impression he wasn't all that jazzed about the assignment. Unit descriptions so clear and concise here become starkly abbreviated there. More than once he misinterprets important field relationships and glosses over findings published by colleagues. Newcomb's writing is hit and miss.

For example, his GSOC abstract on clastic dikes begins with the oddest description of a "typical" dike I've come across,

The vertical section of a typical dike includes an irregular and involved "root" part at the bottom, a central "trunk" part, and an uppermost part where "branches" disperse and taper out.

He suggests the various parts indicate,

...the clastic dikes resulted from upward injections of ground water. Each hydraulic injection probably was caused by bank-storage effluent when a pressure difference was produced by a large lowering of Lake Lewis. Such a lowering occurred after a deterioration of the impounding dam and could have been a repetitious event. The first such lake lowering apparently produced a hydraulic lift and the injection of water into a equidimensional [sic] system of fractures. Later injections used mostly the established transverse dike planes and produced the many laminae of the dikes.

Flooding and diking are related. Chenoweth Creek Valley at The Dalles, OR.

Newcomb's lower "trunk" and rising "branches" imply the dikes ascended from a source layer at depth, though he identifies no such bed in the GSOC abstract or in the several dozen other reports he authored.

Newcomb seems to have overlooked earlier publications (Jenkins, 1925; Lupher, 1944). Works by Jenkins and Lupher contain clear sketches and photographs that depict the dikes in detail. Both authors illustrate filling from above, relationships of the dikes to host strata, and dominantly downward-pinching forms. Both articles were published in prestigious, peer-reviewed journals (American Journal of Science, Geological Society of America Bulletin). Jenkins was a journeyman field geologist employed by various western states, eventually retiring as the Director of the California Geological Survey. Lupher was a professor at Washington State College who went on to become the Supervisor of Field Geology for Shell Oil Company. The guys were pros.

Newcomb also ignored reports published contemporaneously by equally talented colleagues employed by Hanford and the State of Washington (Brown and Brown, 1962; Bingham, 1963). J.W. Bingham described dikes exposed at the most important of Newcomb's field sites, the White Bluffs,

The clastic dikes in the Touchet [Beds] have long been known, but new exposures in the Pasco Basin show the dikes to have a polygonal pattern in plan view, which suggests shrinkage, possibly by drying. Also, several localities were found where clastic dikes of the Touchet-type materials have penetrated the underlying [Plio-Pleistocene] caliche and [Pliocene] Ringold Formation as much as 150 feet.

Pleistocene dikes intrude Tertiary sediments. Typical sheeted clastic dikes filled with Touchet Bed sediment intrude downward into oxidized sands of the Ellensburg Formation at Snipes Mountain, WA. Identical dikes intrude several other formations that underlie Missoula Flood deposits at dozens of locations in Eastern Washington. My photo.

Why didn't Newcomb just quote his colleagues' publications? I can think of three possible reasons.

1.) Clastic dikes had no significance to Newcomb. He viewed them as little more than geological curiosities.

2.) Maybe he observed a few upward-tapering halves of dikes, recalled his schoolbook lessons that taught all dikes are liquefaction features, and decided these are too. Did he never observe the dikes' fluted interior walls or young dikes intruding older deposits? For a guy who spent so many years working these sediments, I find this explanation difficult to accept.

3.) Perhaps Newcomb was working from notes by Richard Foster Flint, an aging but still towering figure at USGS and Yale University. Years earlier, Flint had hastily surveyed the Cheney-Palouse scablands and even ducked into the Walla Walla Valley for a brief look around. There, he named the Touchet Beds at their type locality (Flint, 1938), the bluffs of the Walla Walla River south of Touchet, WA, noting the presence of "sedimentary dikes",

The Touchet beds commonly exhibit zones of warping and folding, and very commonly are cut by faults and sedimentary dikes. Intense folding, including miniature recumbent folds and overthrusts, is confined to thin zones, a few inches to a few feet in thickness, of fine-grained sediment. As these zones are underlain and overlain by non-deformed beds, they are the result of contemporaneous deformation, probably by slumping and sliding of water-saturated silty on gentle subaqueous slopes. Similar phenomena have been observed in glacial lake deposits in other regions. The Touchet silt and sand along lower course of the Snake River, near its mount, lie in broad gentle undulations affecting series of parallel beds up to 20 or 30 feet in thickness. The undulations are 20 to 100 feet long, and have amplitudes up to 10 feet. Their axes are generally transverse to the Snake River. These structures, too, may be the result of flow affecting the silts, possibly analogous to the 'mud lumps' [sand blows] off the mouth of the Mississippi River.

But Flint was an outsider with little experience in south-central Washington. His 1938 notes on the dikes are clearly half-baked and appear to reflect his experience with different dikes from other regions. What's strange is that Newcomb seems oblivious to their preliminary nature. Was he reluctant to disagree with his superior? Did he not think to run Flint's ideas by his peers - about a half dozen men mapping in Eastern Washington at the time? Was he a loner? Is this another case of USGS arrogance raising its ugly head?

To date, no evidence supports an upward dewatering origin for clastic dikes in the Touchet Beds. Sadly, Newcomb's Folly has been promulgated by a number of Hanford-affiliated authors for the past six decades (Campbell, 1962; Bjornstad, 1990; Reidel et al., 1992; Bjornstad and Teel, 1993; Bergeron et al., 1997; Bjornstad and Lanigan, 2007; Apted, 2017). While there is always room for nuance and difference of opinion, these authors, like Newcomb, are just flat wrong.

Look for both halves, fluting, and a source bed. Left: Two legs of a diabase dike intruding granite pinch out in opposite directions at Winter Harbor, ME. Right: Doubly-tapering legs of a clastic dike in the Touchet Beds at Cecil, OR. The mechanics are much the same for both magmatic and sedimentary dikes. One half tells you nothing. Closer inspection required. First excavate the top and tail as best as you can, next identify any fluting on skin walls (directional indicators), then find the source bed, and last speculate on origin. Avoid folly.

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