We set sail under a gentle breeze from the S.E. At seven miles, passed a white clay marl or chalk bluff. Under this bluff, which is extensive, I discovered large stone much like lime, encrusted with a clear substance which I believe to be cobalt, also ore is embedded in the dark earth resembling slate, but much softer.
Above this bluff, we had the prairie set on fire to let the Sioux see that we were on the river, and as a signal for them to come to it.
Captain William Clark ~ 27 August, 1804