Sifting through the Clues

masthead saying 'We Proceeded On'
Reprinted from We Proceeded On1

Lava-Pumice Specimens

Lewis and Clark lava pumice specimens

one gray and one rusty rock

Photo by author

The two surviving rock specimens from the Lewis and Clark Expedition are Seybert Collection No. 534 ("pummice stone," at right) and ANSP 3916/ex Seybert Collection No. 535 (left), which was described by Lewis as "lava" (a volcanic rock) based on its twisted, ropy appearance, but it's a piece of metamorphosed sedimentary rock. Although the captains consistently misidentified these types of rocks throughout the expedition, Lewis and Clark should be credited with disproving the belief that active volcanoes existed in the Louisiana Territory because they deduced the causal relationship between burnt coal beds and adjacent layers of baked and fused rock along the Missouri River.

Lewis and Clark selenite specimens

Glass-like slices of rock

Photo by author

Lewis and Clark collected several specimens of selenite, a clear, colorless variety of gypsum that occurs in clays. Three of these specimens were definitively collected on the expedition: the specimen second from the right in the top row (Seybert Collection No. 799), the specimen second from the left in the top row (Seybert Collection No. 804) and the specimen to the extreme left in the bottom row (Seybert Collection No. 803). The other specimens seen here are presumed to have been collected by Lewis and Clark because they are found in association with the known expedition specimens in the Academy of Natural Sciences collections.

In the journals, the captains' identification of lava was never correct, nor were their nearly 20 "pumice" or "pumicestone" observations actually related to active volcanism. Unlike today's restricted definition, which classifies pumice as a volcanically derived vesicular glassy rock, the captains' characterization of pumice apparently included any fused or baked rock (termed "clinker"), which explains why they most consistently noted its occurrence in regions where coal beds had burned and slightly metamorphosed the adjacent rock strata. Lewis deftly recognized this causal relationship when he composed a cleverly concise comment to accompany the "Lava & pummice Stone" specimen (Fort Mandan mineral specimen No. 67) sent back from Fort Mandan:

"The tract of Country which furnishes the Pummice Stone seen floating down the Misouri, is rather burning or burnt plains than burning mountains."2

Air pockets in pumice stones and similar rocks can make them light enough to float.

Selenite Specimens

Of the three documented mineral specimens identified as selenite (a clear, colorless variety of gypsum), it appears that the specimen labeled Seybert Collection No. 799 corresponds to Fort Mandan mineralogical specimen No. 6 because of its unique cross-like shape (technically termed "twinning") and its documented date of collection of August 23, 1804. Seybert's appended description of two other selenite specimens (Seybert Collection Nos. 803 and 804) may be in error because they were described in his circa 1812 catalogue as "Crystallized sulphat of Lime. Calumet Bluff. Missouri. Captn. Lewis," which would place their date of collection between August 28 and September 1, 1804; according to the Fort Mandan mineralogical specimen list in the A.P.S. donation book, there were no minerals collected in that time frame matching Seybert's "sulphat of lime" description. This includes those specimens that mention Calumet Bluff in their listed description (Fort Mandan mineralogical specimen Nos. 22 and 34) or that were identified as collected on September 1, 1804 (Fort Mandan mineralogical specimen No. 15) or from adjacent areas of "white Chalk Bluffs" or "white <Chalk> Clay Bluffs" (Fort Mandan mineralogical specimen Nos. 3, 43, 52, and 53).

Additionally, each of the expedition minerals identified by Seybert, in whole or in part, as a "sulphat of lime" have recorded dates of collection indicating they were not gathered in the locale of Calumet Bluff; these include Fort Mandan mineral specimen No. 6 (collected on August 21, 1804), specimen Nos. 13, 20, and 49 (August 22, 1804), specimen No. 8 (August 23, 1804), and specimen No. 35 (September 4, 1804, based on mention of the Quicurre [Niobrara] River). The description of the remaining "sulphat of lime" specimen is too imprecise to be specifically assigned only to Calumet Bluffs (Fort Mandan mineralogical specimen No. 63, described as a "Specimen of a Substance extremely common & found intermix'd with the loose Earth of all the Cliffs & Hills from the Calumet Bluff to Fort Mandon").

In summary, it appears that Seybert erred in assigning the specimens labeled as Seybert Collection Nos. 803 and 804 exclusively to an area near Calumet Bluff. Based on the information recorded in the A.P.S. donation book, these two specimens could have been collected as far downriver on the Missouri as the confluence with Floyd River (where the expedition departed on the morning of August 21, 1804) and as far upriver as Fort Mandan. As such, the description of the provenance of these specimens in future A.N.S. literature should be expanded to encompass a wider range of the potential collection localities.

Difficult Answers

To this day, most of the specimens sold by Seybert to the A.N.S. in 1812 remain segregated from the academy's general collection of minerals—they are kept in a cabinet built for them circa 1825.3 Could the cabinet perhaps hold samples collected on the expedition? That's unlikely, because a catalogue of the Seybert collection compiled in 1825 (representing the specimens in the cabinet) lists 157 fewer specimens than the catalogue Seybert compiled circa 1812. One can reasonably assume that among the 157 missing specimens were those collected on the expedition, because nowhere in the 1825 catalogue is there any reference to Lewis or Clark. All or most of these 157 specimens— including those collected by the captains—were probably integrated into the academy's general mineral collection between 1812 and 1825.4

Do any Lewis and Clark specimens still exist in the A.N.S.'s general collection? It is a difficult question to answer because the academy eventually reorganized its collection, placing its non-mineralogical rock and sediment samples in a separate "petrologic" collection. Many, if not most, of the samples collected by Lewis and Clark would be classified as petrologic. In 1993, the academy's petrologic collection was formally transferred to another Philadelphia institution, the Wagner Free Institute of Science.5 At the time of the transfer, the academy transcribed complete information from every label in the collection; no references to Lewis or Seybert were found.6 In principle, an expert in western mineralogy could examine the Wagner specimens and identify those representative of formations along the explorers' route.7 Unfortunately, the entire collection was crated and placed in storage, making it inaccessible to researchers at the present time.

Tantalizing Possibilities

The captains may have collected other mineral and fossil specimens unaccounted for in the expedition literature or at the Academy of Natural Sciences.

Samuel George Morton, a physician and amateur paleontologist, makes tantalizing reference to expedition related fossils in a number of articles published between 1830 and 1842. In one, for example, Morton notes that "Lewis and Clark, in their expedition to the Columbia river, procured a few fossils at the great bend of the Missouri river."8 Morton has the captains collecting invertebrate fossils such as Baculites (an extinct cephalopod) and Gryphaea (an extinct oysterlike mollusk).9 Unfortunately, neither of these was listed in the Fort Mandan shipment or in the A.P.S. donation book, and they do not appear in Peale's museum accession book or Seybert's inventory catalogues. Perhaps the fossils mentioned by Morton have a separate, unknown history of collection and disposition, or maybe he just erred in crediting the captains with these discoveries. A resolution to this question awaits the discovery of written documentation substantiating a Lewis and Clark provenance.

  • 1. John W. Jengo, "'Specimine of the Stone': The Fate of Lewis and Clark's Mineralogical Specimens," We Proceeded On, August 2005, Volume 31, No. 3, the quarterly journal of the Lewis and Clark Trail Heritage Foundation. Editorial additions include page titles, side headings, and graphics to assist the web-based reader. The original format is provided at
  • 2. Moulton, Vol. 3, 478. Lewis also commented under Fort Mandan mineralogical specimen No. 62 that "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 . . . . . 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." [A reference to Fort Mandan mineralogical specimen No. 67.]
  • 3. Spamer, et al., 50.
  • 4. To explain their absence from the 1825 catalogue, some have hypothesized that Seybert did not include the Lewis and Clark specimens in the collection he sold to the A.N.S. in 1812. (Greene and Burke, p. 39.) But the A.N.S.'s general collection contains specimens included in the circa 1812 catalogue, indicating that at least some, if not all, of the Lewis and Clark specimens were part of the collection purchased from Seybert. More likely, the absence is due to their probable removal from the Seybert collection sometime before the 1825 recataloging.
  • 5. Spamer, et al., 51.
  • 6. Spamer, personal communication, June 19, 2002.
  • 7. At least one specimen—the shonkinite rock collected on May 31, 1805—would be readily identifiable because of its rarity and unique mineralogy; see John W. Jengo, "'high broken and rocky': Lewis and Clark as geological observers," WPO, May 2002), 22–27. Also, John W. Jengo,"'Broken Masses of Rock and Stones': Lewis and Clark as Geological Trailblazers," The Professional Geologist, Vol. 39, No. 10 (November 2002), 2–6.
  • 8. Samuel George Morton, "Description of Some New Species of Organic Remains of the Cretaceous Group of the U. States: With a Tabular View of the Fossils Hitherto Discovered in That Formation," Journal of the Academy of Natural Sciences, Vol. 8 (Philadelphia: Merrihew and Thompson, 1842), 3. Thanks to Ella Mae Howard for bringing Morton to my attention.
  • 9. Samuel George Morton, Synopsis of the Organic Remains of The Cretaceous Group of The United States. Illustrated by Nineteen Plates. To Which is Added An Appendix, Containing a Tabular View of The Tertiary Fossils Hitherto Discovered in North America (Philadelphia: Key & Biddle, 1834), 25.