The Great Wind-or-Water Debate

B.Shimek wasn't the only one who could smartly analyze snail data. In fact, long before Shimek's 1902 paper using Natchez snails to prove that loess was wind-deposited, Raphael Pumpelly in a landmark 1879 paper had made the argument that loess was wind-deposited. He'd studied loess in China and America and come to all the right conclusions. Similarly, long before Shimek, Boston snail specialist Amos Binney had  recognized that the snail species found embedded in loess were forest-litter species, not streambed ones. However, Binney continued thinking, along with Sir Charles Lyell, that  loess was water-deposited.

However, the fine work of these two great scientists had made little impact on geology's big guns... such as our Sir Charles Lyell. Unfortunately, in science, as in nearly everything else, having good timing is often more important than having mere genius.

The debate was still going on in 1942 when G.D. Smith published a paper on Illinois loess. In about forty localities Smith measured how deep the loess was, and he found out this: That loess was thickest near the river, and got thinner away from it. Moreover, like so many grand phenomena presided over by elemental laws of nature, the rate of thinning out was beautifully, even exquisitely, predictable, and could be expressed with sublime succinctness. Smith said that the rate of thinning was a linear function of the logarithm of the distance from the source.

Doesn't this sound like something being deposited systematically by a great mass of unencumbered wind advancing majestically across the land, and not by the irreverent, unpredictable currents, vortexes, and eddies of flowing water?

Of course, not everyone was transfixed by the powerful image of a continent besieged by dusty wind. In 1944, two years after Smith's publication, respected geologist R.J. Russell declared that loess was ordinarily as well developed on one side of a ridge as on the other, so it couldn't possibly be explained by a hypothetical wind blowing in a prevailing direction. He further claimed that the sorting of loess particles was too uniform to be explained by either the deposition of wind or water, and that, based on his own field observations, especially with regard to stratigraphic relationships, wind just didn't seem to have anything to do with the whole matter.

Today some people look at this famed geologist's assertions and scratch their heads...

But Russell wasn't the only one doubting the clear logic of Shimeck's snails and Smith's mathematical insight. In quick succession one publication after another appeared supporting one side or the other -- wind, water, or something else -- and sometimes experts even declared the whole matter finally to be explained and settled, but then always other famous experts holding just as many academic degrees would insist that just the opposite was true.

Years passed, but no single great discovery ever settled the issue. Not even to this day.

Nevertheless, today the world of science pretty much agrees that loess has been deposited by wind. Some geologists might still be found who debate some parts of the story we can tell, but the central facts in the loess story are no longer seriously in doubt. Shimek and his snails have been right all along. Loess is deposited by wind.

One reason the story has been slow in coming was that the mystery of loess could never be explained by focusing merely on the loess itself. Loess, it turns out, is merely a relic, a sideshow, associated with an event in geological time so enormous, so enigmatic, so charged with continent-shattering energy, that it is hard for us in our every-day world to imagine. To sit in a steamy swamp in the Lower Mississippi Valley and imagine this outrageous event simply requires enormous brain bending.

But, that story happened.

If you'd like to know more, then return to the What is Loess Menu, and keep on reading, now about Carbon 14 and some more snails...

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