Pumice - Specimen

Lewis's specimen of pumice

A specimen of pumice believed to have been sent to
President Jefferson
Photo courtesy of the Academy of Natural Sciences, Philadelphia
Richard M. McCourt, Curator

Among the numerous papers and collections shipped back east from Fort Mandan on the keelboat in April of 1805 was a mineralogical collection of sixty-eight specimens. Lewis's list of the collection's contents is among the "Fort Mandan Miscellany,"1 but only seven of the existing specimens remain, and only one of those, a "Petrified Jawbone of a fish" found by Sergeant Gass on the Missouri River in August of 1804, still has the original label attached. The provenance of the rest cannot be verified.

Three of the sixty-eight descriptions in Lewis's list are of interest in the present context. Number twenty-four was "Carbonated wood found on the Std. side of the Riv near fort mandane 60 feet above high water mark in the Bank Strata 6 Inch thick." Number sixty-four was "Specimen of Carbonated wood with the loose Sand of the sand-Bars of the Missouri & Mississippi, it appears in considerable quantaties in many places." The whereabouts of those specimens are currently unknown.

The third is number sixty-two. Lewis's annotation in the list reads:

Specimen of the pummice stone found amongst the piles of drift wood on the Missouri, sometimes found as low down as the mouth of the osage river. I can hear of no burning mountain in the neighborhood of the Missouri or its Branches, but the bluffs of the river are now on fire at Several places, particularly that part named in our chart of the MissouriThe Burning Bluffs.2 the plains in many places, throughout this great extent of open country, exhibit abundant proofs of having been once on fire . Witness the Specimens of Lava and Pummicestone found in the Hills near fort mandon...

Unfortunately, the association between that description and the specimen pictured above is only anecdotal.

Clearly, Lewis confused cold coal clinker with pumice. But the riddles of the earth's crust, and of the fire at the core, were yet to be solved by geologists--who in the decade of the Expedition had not even agreed upon the name of their science.


1. Moulton, ed., Journals, 3:472-378.

2. This may refer to either the "Mineral Bluffs" or the "Hot Bluff" shown upstream from the Big Sioux River, on the map Clark drew at Fort Mandan during the winter of 1805.