He published an account of the incidents of this exploratory journey, under the title of _Travels in the Central Portions of the Mississippi Valley_.

He found, in passing up the river _Des Plaines_, a remarkably well characterized specimen of a fossil tree, completely converted to stone, of which he prepared a descriptive memoir, which had the effect further to direct the public mind to geological phenomena.
We are not prepared to pursue minutely these first steps of his energetic course in the early investigation of our natural history and geography.

In 1822, while the lead-mine problem was under advisement at Washington, he was appointed by Mr.Monroe to the semi-diplomatic position of Agent for Indian Affairs on the North-west Frontiers.

This opened a new field of inquiry, and, while it opposed no bar to the pursuits of natural science, it presented a broad area of historical and ethnological research.

On this he entered with great ardor, and an event of generally controlling influence on human pursuits occurred to enlarge these studies, in his marriage to Miss Jane Johnston, a highly cultivated young lady, who was equally well versed in the English and Algonquin languages, being a descendant, by the mother's side, of Wabojeeg, a celebrated war sachem, and ruling cacique of his nation.