Tuesday, January 24, 2023

Mssr. Nicollet & I consider Glacial Theory in northeast South Dakota

Courtesy NASA.

During my visit to northeast South Dakota last fall, I bumped into the great surveyor Joseph Nicollet and discovered we had similar goals. As aspiring geologists we hoped to expand our knowledge of the discipline. We wanted to see and understand the magnificent Coteau des Prairies. And we both struggled to picture today's prairies buried under a thick sheet of ice, though for different reasons.

Thanks to some deep memory, I knew eastern South Dakota was once glaciated but had given the subject little attention. In contrast, glaciation (or rather its possibility) was of great importance to Nicollet, but he didn't know what to think. It was very difficult to accept on such a scale. Our contrasting reactions were understandable given our visits were 183 years apart.
Nicollet Tower near Sisseton, SD. I "met" Joseph Nicollet in the interpretive center at the base.
In 1832, at age 46, Joseph Nicolas Nicollet left France for reasons unclear—perhaps political, perhaps financial, or perhaps because he had become passé, démodé. Though widely recognized as one of the best astronomers and surveyors in the country, his skills were no longer in demand. Much of France had been adequately mapped. This was not the case in the United States. Most of the young country remained only nominally surveyed. Existing maps often were unreliable.

To Nicollet, the opportunities were obvious. Even before he departed for the US, he had decided he would survey and map the great triangle between the Mississippi and Missouri Rivers, as far north as Lake Superior—a region of French influence and French speakers. Seriously, monsieur?! How will a slightly-built, well-educated and cultured but penniless Frenchman survive in this wild unsettled territory? Mais qu'importe; he would make it happen.
Portrait of Joseph Nicolas Nicollet, date unknown (source).
Nicollet's area of interest; annotated excerpt from 1969 USGS topographic relief map.
In 1835, Nicollet was in St. Louis, at the confluence of the Mississippi and Missouri, campaigning for a survey of the upper Mississippi. He secured the support of the American Fur Company (always eager for better maps), and the wealthy Choteau family—fur traders and merchants. The next year he traveled by steamboat to Fort Snelling, and from there, surveyed the upper Mississippi drainage by canoe with Ojibway and French-speaking halfbreed guides. Back at Fort Snelling, Nicollet refined calculations of latitude and longitude from his celestial observation data, and produced a map of the territory he had covered. When he returned to Washington DC, he found that news of his excellent map had already arrived.

Among other things, Nicollet fixed errors made 30 years earlier by Army officer and explorer Zebulon Pike. Most egregious was Pike's erroneous placement of the mouth of the Crow Wing River, off by 27' latitude. As a result, everything upstream was too far south and west, contracting "the extensive region between the Mississippi and the Missouri; so that there was not (so to speak) room for the intermediate territories which I had explored." (This and all Nicollet quotes below are from the 1843 report accompanying his map of the upper Mississippi drainage).

Recognizing Nicollet's skill and zeal for accuracy, the US government, through the Army Corps of Topographical Engineers, funded additional survey, and provided an assistant—a young officer just 25 years old named John C. Frémont, the future Pathfinder. It was an excellent investment. Nicollet would lead two expeditions in the upper Mississippi drainage, determine latitude and longitude for some 90,000 points, and produce Hydrographical Basin of the Upper Mississippi River, the first accurate map of the region.
Excerpt from Nicollet's map, published after his death in 1843; blue labels added.

The first expedition, in 1838, went well enough that Nicollet was able to secure funding for a second, to areas farther north, including Devil's Lake (in today's North Dakota) and the intriguing Coteau des Prairies. On April 4, 1839 Nicollet, Frémont, and botanist Charles Geyer left St. Louis aboard the American Fur Company's steamboat Antelope, bound for Fort Pierre 1270 miles upstream. The Missouri was very low and they repeatedly ran aground, sometimes waiting several days for the water to rise. But there were benefits. Whenever the Antelope was firmly stuck, the scientists went ashore in search of discoveries.

Nicollet would climb banks and slopes above the river to study exposed rock layers, often fossil-rich. He hoped to assign them to the stratigraphic classification used in Europe. Intriguingly, east of the river, at the top of slopes where the land flattened, he inevitably found not layered strata but jumbled accumulations of gravel, cobbles, and even large boulders, all derived from rock unlike any in the area. These kinds of deposits—unstratified and distantly derived—had also been described in Europe, where they were called diluvium or erratic deposites (old spelling of deposit).

After 69 days the Antelope finally reached Fort Pierre, on the west side of the Missouri. It had rained heavily the night before, and water was surging off the largely barren land into the river. The wet clay-rich soil was so slimy, soft and sticky that it was impassable, even on foot. Nicollet noted in his journal that travelers reported similar conditions extending far to the west—lands "so sterile that they are referred to as the Great American Desert."

Yet just across the river to the east, the landscapes changed dramatically: "the vast spaces opening to your gaze, the astonishingly richer vegetation, the smoother undulations breaking the monotony, the purity of the water in the streams and rivers flowing into the Missouri, the nature of the woods shading them—everything proclaims a favorable change in the physical aspects of the country."
The "astonishingly richer vegetation" east of the Missouri has been largely replaced with cultivated fields.
After 18 days at Fort Pierre preparing for prairie travel, Nicollet and his party headed northeast. He found the country beautiful and surprisingly novel. "It is neither a mountainous, nor a hilly, nor an absolutely flat country; exhibiting undulations of the surface that are not entitled to these usual appellations." Early explorers, first French, then British, "were so forcibly impressed with this novelty in the appearance of the topography, that they employed new names to designate it. Hence, we have the expressions: Coteau des Prairies, Coteau des Bois, Hauteurs des Terres, and rolling, flat, or marshy prairies."

As they traveled, one geological feature was ever-present—jumbled accumulations of gravel, cobbles, and boulders like those Nicollet had seen earlier above the Missouri River. He described it as "a vast deposite of sand, gravel, pebbles, and clays ... and masses of rocks transported to a distance from their original position, usually called erratic blocks. This deposite always occurs between the vegetable soil and the rocky strata of all ages that constitute the geological basis of each section of country."

Because the deposits were quite jumbled and found immediately below the soil, they probably had arrived recently (geologically speaking). But from where and how? Nicollet hesitated to draw conclusions. "It is difficult to determine the direction whence the materials of the erratic deposite came. The presumption is, judging from the nature of the erratic blocks—the analogues of which are found in higher latitudes—that they were brought from the north to the south." In this presumption, Nicollet was correct.
Erratic blocks as riprap; east shore of Lake Oahe on the Missouri River.
Erratic blocks poking through "vegetable soil" on the Coteau des Prairies.
Nicollet likely knew of erratic deposites prior to his expeditions. In St. Louis in 1835, he met artist and ethnographer George Catlin, who had toured the country west of Fort Snelling as far as the Coteau des Prairies. Catlin was a bit of a geologist himself, curious about the origins of the landscapes he painted. Surely the two men discussed the puzzling deposits, which were of great interest to Catlin. In fact, he presented a paper on the subject to the Boston Society of Natural History.

"There are thousands and tens of thousands of bowlders scattered over the prairies at the base of the Coteau ... I believe that the geologist may take the different varieties which he may gather at the base of the Coteau in one hour, and travel the continent of North America all over without being enabled to put them all in place; coming at last to the unavoidable conclusion, that numerous chains or beds of primitive rocks have reared their heads on this continent [these are uplifted mountains], the summits of which have been swept away by the force of the diluvial currents, and their fragments jostled together and strewed about, like foreigners in a strange land ..." (Catlin 1840; emphasis mine).
The great Deluge in northern Europe (Figuier 1863).
Several of Catlin's "foreigners in a strange land" at Sica Hollow State Park.
Catlin's thinking was shaped by the widely accepted Diluvial Theory, which proposed a catastrophic flood of global proportions. The strongest evidence came from the Bible; without biblical narratives, such an immense and powerful flood would be difficult to justify.

However by the time Nicollet was studying erratic deposites in North America, a new theory had come to the fore. Louis Agassiz's Glacial Theory nicely explained why features associated with today's glaciers—striations, polish, erratic deposites, and such—were also found far from any ice. During "glacial epochs" or "ice ages", when the Earth's climate was much colder, glaciers and ice sheets extended lower in elevation and farther south.

But climate change and ice ages were radical new ideas, and very difficult to accept. Poor Nicollet had to write his report in the midst of a raging debate—Diluvial vs. Glacial. Wisely, he described the vast erratic deposites but took no position on their origins. "The region comprised within my map is covered by species of deposite of the kind for a long time known by the name of diluvium; but as this word implies a theoretic idea as regards the accumulation of such deposites, the cause of which is still open to controversy, it is now very generally abandoned, and the designation of erratic deposites, among others, adopted in its stead. I have, therefore, used the latter expression ..."

Perhaps you are wondering, as Nicollet surely did, whether the erratic deposites east of the Missouri River explain the lush prairie grasses there. If so, how did the Great American Desert to the west escape the flood? Or was it an ice sheet? How nice if Mssr. Nicollet's spirit were following this blog. He would soon learn of today's thinking about erratic deposites. And he might be pleased to know that for the wonderful Coteau des Prairies, le mystère demeure.
 "The head of the Coteau is very near us. It presents an imposing mass ... beautiful to the eyes which have seen nothing but plains and rolling plateaus. It is the Alps of this region." (Coteau from north, by Bigfitz79)


Bray, MC. 1970. Joseph Nicolas Nicollet, geologist. Proc. Am. Phil. Soc. 114:37-59.

Bray, MC. 1980. Joseph Nicollet and his map. American Philosophical Society, Philadelphia.

Catlin, George. 1840. Account of a journey to the Coteau des Prairies, with a description of the red pipe stone quarry and granite boulders found there: Am. Jour. Sci., 1st ser., v. 38, p.138-146.

Figuier, L. 1863. (Bristow, LH, ed. 1872). The World Before the Deluge. Accessed Jan 2023.

Hansen, B. 1970. The early history of glacial theory in British geology. J. Glaciology. Accessed Jan 2023.

Johnson, WC, and Knight, DH. 2022. Ecology of Dakota Landscapes; past, present, and future. Yale University Press (reviewed here).

Nicolett, JN. 1843. Report intended to illustrate a map of the hydrographical basin of the upper Mississippi river. US Senate, 28th Congress, 2nd session, no. 237. Accessed Jan 2023. A high-resolution zoomable version of Nicolett's map is available online.


  1. South Dakota is an amazing state, as are the other states and areas within and around Nicollet's "great triangle." Interesting to study the history of the glaciers, for sure. They definitely affected the landscapes and other aspects of Wisconsin. The Driftless Area wasn't covered during the last ice age, so it has an entirely different topography.

    1. I agree, Beth. It was wonderful to see the legacy of continental glaciation, a new experience for me (vs. mountain glaciers). It would be neat to check out the driftless area ... I can appreciated it now.