The determination to penetrate to the source of the Mississippi, during the summer months, made an early departure important. I had, while at Potosi, in Missouri, during the prior month of February, written to Hon. J. B. Thomas, U. S. S., Washington, to endeavor to secure an appointment to explore the mineralogy and natural features of the upper Mississippi River; and as soon as I had published my treatise on the mines and minerals of Missouri, I proceeded to Washington, and submitted to the proper officers of the Government, my account of the mineralogical wealth of the western domains, with a plan for the management of the public mines. Mr. Calhoun decidedly favored these views; but, foreseeing the necessity of congressional action on the subject, and the necessary delays of departmental references, said to me, that he had just received a memoir from Governor Cass, of Michigan, proposing an expedition to the source of the Mississippi, to leave Detroit early in the spring, and offered me the position of mineralogist and geologist on that service. This agreeing, as it did, with my prior views of exploring the public domains, I gladly accepted, and immediately returned to the city of New York to prepare for the journey. The year 1820 had commenced with severe weather, the Hudson being frozen hard, as high as West Point, on the 1st of January; and there was a fall of snow between the 10th and 11th of February, which laid four feet deep in the streets of New York. March opened with mildness, and every appearance denoted an early spring, which led me to hasten my movement north. I left New York on the 5th of March, in the citizens' post-coach, on sleighs, for Albany, taking the route through Westchester, and over the Highlands of Putnam and Dutchess; sleeping at Fishkill and Kinderhook, the first and second nights, and reaching Albany on the morning of the 7th, a distance of one hundred and sixty miles. This distance we made in forty hours actual travelling, averaging four miles per hour, incidental stops included, which is about the rate of travelling by the trekschuits of Holland,[6] and by sledges over the frozen grounds of Russia.[7] In crossing the Highlands, some one, in the change of the stage-sleighs, pilfered a small box of choice minerals which I set store by; the thief thinking, probably, from the weight and looks of the box, which had been a banker's, that it was still filled with coin. We crossed the Hudson from Greenbush, in a boat drawn through a channel cut in the ice. Snow still laid in the streets of Albany, and a cold north wind presaged a change of temperature. Next day there was a hail-storm from the northwest, with rain and sleet, and on the morning of the 9th, the hail lay six inches deep in the streets. In the evening, proceeded by stage to the city of Schenectady, a distance of sixteen miles, across the arenaceous tract of the Pine Plains, by a turnpike,