Jim Bradshaw: Anthills, aborigines and mounds on the prairie

In the spring of 1851, editor Daniel Dennett sold the Planters’ Banner, the newspaper in Franklin, and set out for Texas, where he intended “to follow agricultural pursuits, as a more reliable means of support” than running a country newspaper.
He wrote a series of letters describing his trip across south Louisiana, and in two of them described thousands of mysterious mounds found on the south Louisiana prairies and in our pine forests. They range from about 30 to 50 feet in diameter and three to seven feet tall, and are known to scientists as Mima or pimple mounds.
Dennett speculated they were “the work of aborigines,” but that has never been proven. Theories abound, but geologists and soil scientists are still arguing about how the mounds might have been created.
“As we advanced westward … from Vermilionville to the Calcasieu [River],” Dennett wrote, “the prairie became more thickly dusted with them, and in most places west of the Mermentau they may be seen in thousands.”
He said the mounds sometimes appeared to be in rows, “but in most instances their position and appearance have a striking resemblance to … villages, a circle being formed by twelve or thirteen mounds.”  He thought “their numbers in these prairies may be reckoned in the millions.”
Dennett thought the mounds were very old because large trees grew on them “as though their origin dates back far beyond the origin of the trees.” Traveling through the pine forest between the Calcasieu and Sabine rivers, he found “great numbers of mounds similar to those noticed in the prairies” and thought that “from their appearance they must have been here long before the present forest commenced growing.”
Dennett was apparently aware of theories that ascribed their origin to natural causes such as glaciers burrowing underground during the Ice Age, or wind-blown soil being caught by clumps of prairie grass and gradually enlarging, but he would have none of that.
“That they be the work of the aborigines of this country I have no doubt,” Dennett wrote. “That nature formed them to me appears perfectly absurd.”
E. G. Hilgard, one of the leading soil scientists of his day, dug into mounds on the Opelousas and Calcasieu prairies in the early 1900s and also thought they were quite old. But he thought they were made by ants, not aborigines.
He said the way the mounds were formed ruled out glacial or wind-blown origins, and, according to an article written in 1906, “I therefore … considered the ant-hill origin as the only reasonable explanation.”
In more recent times, geologists and archaeologists have come to think that mound-building ants are probably not the answer, but are just as divided over what the real answer is.
They have not ruled out the glacial and wind-blown soil theories, and have proposed novel new ones, including the idea that they were formed by vibrations from ancient earthquakes.
The science for that one is a little beyond what I have retained from the Earth Science 101 course I took way back when, but I’m pretty sure of what Daniel Dennett would say about it.
 A collection of Jim Bradshaw’s columns, 'Cajuns and Other Characters,' is now available from Pelican Publishing. You can contact him at jimbradshaw4321@gmail.com or P.O. Box 1121, Washington LA 70589.