Rocks and Fossils

Lewis and Clark as Geologists and Fossil Collectors

Sergeant Gass's Discovery

Sgt. Gass's Discovery

The Academy of Natural Sciences of Philadelphia

The geological observations of the Lewis and Clark expedition have suffered from a tradition of being dismissed as inconsequential, sporadic, and largely unhelpful in studying the geology of the American Northwest. But a thorough, recently published review by John Jengo admirably demonstrates that this is not the case. Not only did the explorers give thoughtful attention to geological phenomena, but modern geological perspectives can glean a lot from what might seem to be cursory observations written into the journals.1

Suffice it to say here, Lewis and Clark were of course not geologists. But inasmuch as astronauts who first explored the moon were not geologists either (except for one of them, Harrison Schmidt, who flew on Apollo 17), proxy training goes a long way when an expedition ventures to where no professional has gone before. So here again, Lewis, by dint of his tutoring in Philadelphia, was in charge of observation—and yet, ironically, the only two significant paleontological discoveries of the expedition were made by Patrick Gass and William Clark. But they did not restrict their efforts to static observation; they even experimented, conducting crude mineralogical and chemical tests on coals, pumice, and mineral waters.

Still, the paleontological observations made during the expedition were few and far between. As John Jengo explained in defense of the men, this was due more to nature than oversight or disinterest:

Certainly, the nature of fossil deposits in the West were one of the principal reasons more specimens were not collected. For the most part, fossils in the West are deeply imbedded in solid rock, often disarticulated, and rarely exposed in their entirety; thus, they require a considerable amount of time to locate and remove for study, a luxury that Lewis and Clark could simply have not afforded.2

While this is precisely true, it also repeats a common bias in paleontological collecting for vertebrate remains, because fossil bones are often far more appealing and inspirational than all but the largest, most aesthetic invertebrates. Perhaps this also reflected the focuses of the mentors, selected by Thomas Jefferson to instruct Lewis in many subjects. And of course, still fresh in everyone's minds were the exciting recent developments with the Megalonyx, not to mention anything to do with mastodons and mammoths, and the ever-present idea that these animals might be spotted alive.

Lewis and Clark's fossil finds

Lewis and Clark's notices and collections of fossils from the transcontinental expedition are meager—virtually negligible—in comparison to the wealth of other materials returned by the expedition. But nevertheless the explorers did make some finds and observations. The first fossil they found was observed on 10 September 1804 in southeastern South Dakota. Clark, who reported it in his journal without mentioning who saw it, wrote: "below the [Cedar] Island on the top of a ridge we found a back bone with the most of the entire laying Connected for 45 feet those bones are petrified, Some teeth & ribs also Connected." Actually, these were not the remains of a fish but of a Mesozoic, aquatic reptile which since the early 1820s has been called a plesiosaur. It is believed that some of those fossils are now in the Smithsonian Institution.

On 6 August 1804, Sgt. Patrick Gass found the one fossil known to survive from the expedition today. He did not mention it in his journal (nor did either of the captains in their journals), but the data were recorded by Lewis on a tag that accompanied the specimen to Philadelphia. It accompanied the so-called Fort Mandan shipment, the first batch of specimens to be sent back East from Fort Mandan, in 1805. Gass's discovery was near Soldiers River, which flows in Harrison County, Iowa, in (we know now) strata dated to the Cretaceous Period. The original label indicates that it was collected in a "cavern," but this is more likely to have been an undercut in the stream bank rather than an underground passage.

The fossil seems to have been found in place, not washed out of the sediment. Many fossils may be discovered after storms expose them, and in this regard it is interesting to read that in Clark's journal for 6 August he reported a "Violent Storm" the preceding night. Gass commented on it, too, as did the other journal keepers in the expedition except Joseph Whitehouse; yet oddly enough, Gass did not mention his hunting trip up Soldier River (although as a rule his journal entries were brief). Even so, the storm might have just exposed enough of Gass's fish fossil that night to attract the sergeant's attention.3

In any case, the first formal notice of the fish fossil did not appear until it arrived in Philadelphia late in 1805, when it was listed as item No. 9 in the "Donation Book." The label, in Lewis's own handwriting, reads: "Petrifed Jaw bone of a fish or some other anamal found in a cavern a few miles distance from the Missouri S side of the River. 6 Aug. 1804." ("S" meaning the starboard or right side of the river as they moved upstream, following the convention used at the time).

The specimen itself is rather unremarkable in appearance; a fragmentary right upper jaw, black, with a few small, sharp, beveled teeth. Not until twenty years after the expedition was it even identified, but then as a new genus and species of fossil fish, Saurocephalus lanciformis ("spear-shaped lizard-head," referring specifically to the tooth style in this new kind of "lizard-headed," or lizard-jawed, fish). Richard Harlan described it in a short paper published in the Journal of the Academy of Natural Sciences of Philadelphia for 18244 and as such he is the only person to have described any fossil species from the collections of Lewis and Clark. That it was entirely new to science was additionally remarkable. The species was interesting enough to be mentioned as a side note in a scientific paper on another subject by the eminent English geologist William Conybeare (1787-1857), who said that it formed "an important addition to the very interesting class of fossil Sauri."5 He specially noted that the species had not yet been found in England, revealing a prevalent scientific undercurrent that fauna discovered in America must be represented in the Old World, too.

Geological and paleontological studies in America had previously been restricted largely to the coal regions of the Appalachians, and to the unconsolidated sediments of the Atlantic Coastal Plain (particularly the seaboard region accessible to the researchers who lived between about the Carolinas and northern New Jersey). Samuel G. Morton (1799-1851) was another Philadelphia-based physician-geologist who had taken up the study of fossils in the Coastal Plain, using them to ascertain the relative ages of the geological formations there. The information that came from the West provided the first definitive proofs of the sequence of geological formations there, which indicated their ages relative to similar formations in the East. In 1834 Morton made passing reference to Lewis and Clark's fossils, although no vertebrates were mentioned by name:

Messrs. Lewis and Clarke [sic], Mr. Nuttall and Col. Long, found Baculites, Gryphaea and other marl fossils at the Great Bend of the Missouri river, (lat 43°40' N., long. 72° W. from Washington), intimating the existence of the Ferruginous sand in that remote region of our continent.6

Here Morton implied a Cretaceous age for Lewis and Clark's fossils. The "ferruginous sand" is the greensand marl7 that is abundant especially in the New Jersey coastal plain; it is a distinct stratigraphic horizon, composed principally of the clayey, green mineral glauconite, a Cretaceous-age stratum recognizable to geologists in the eastern United States as well as in England. On page 29 of his publication Morton also made passing reference to Saurocephalus lanciformis when he described the specimens of another fossil fish, Saurodon leanus ("Lea's lizard-tooth"): "These remains appear to be congeneric with the Saurocephalus of Dr. Harlan . . . brought from Missouri by Messrs. Lewis and Clark." Thus the Lewis and Clark specimen is the first documented example of paleontologically based correlation between strata in the eastern United States and the region west of the Mississippi River.

Dinosaur Toes

Dinosaur toes

Courtesy The Academy of Natural Sciences of Philadelphia, Department of Vertebrate Zoology

These fossils were found in the Hell Creek Formation near Fort Yates, North Dakota by Edward D. Cope and party in 1893.

William Clark noted in his journal that while his men were retrieving the two bighorn sheep they had just shot, he spent the time in prying pieces of "the rib of a fish" from a cliff along the Yellowstone River.

this rib is [blank] inches in Secumpherance about the middle it is 3 feet in length tho a part of the end appears to have been broken off I have Several peces of this rib the bone is neither decayed nor petrified but very rotten. the part which I could not get out may be Seen, it is about 6 or 7 Miles below Pompys Tower in the face of the Lard. Clift about 20 feet above the water.

Evidently Clark was on the lookout for fossils. The one he found was in the uppermost part of the Hell Creek Formation, a Cretaceous layer (144-66 million years ago) well-known today for its dinosaur remains. Common dinosaurs of the period in this region were Edmontosaurus, Triceratops and Tyrannosaurus.8

It is now believed that his "fish" was actually a limb bone of a dinosaur. Apparently, the specimen did not survive the journey home. Very likely it soon crumbled beyond recognition, so Clark discarded it before the end of the expedition, or shortly thereafter. Nicholas Biddle, who edited the journals for the first printing in 1814, filled in the circumference—"about 3"—during an interview with Clark in 1810.


No one of the expedition—nor even Wistar or Cuvier for that matter—knew anything of dinosaurs. Although bones such as these had been collected in America, England, and Europe, they were enigmatic; these denizens of such great modern popularity had not yet been scientifically described. The term "dinosaur" would not be created for another four decades, when English paleontologist Richard Owen systematically recognized this special group of reptiles.

Whereas most people might expect fossilized bone to be dense, hard material, some remains when exposed to the elements will be chemically and physically reduced to their mineralogical components, yielding a "rotten" texture and appearance.

In addition to these two notable specimens, the 1805 Fort Mandan shipment did include a few other specimens, all but one lost now. Does this mean that this was all that the Corps collected? Probably not. We might conclude that no attempt was made to collect any "representative set" of fossils in any fossiliferous locales that they encountered, perhaps only for lack of space. Precise "stratigraphic control" of collections was unusual at the time, too; this standard procedure of fossil collecting was not yet widely used. It is the careful documentation of where fossils are found with respect to the tops and bottoms of the layers they are found in, as well as their exact geographic location. But, ironically, because the Lewis and Clark expedition is so well studied even such scant information as the date provides enough information to locate their approximate geographical location on modern maps. In turn, the information can be transposed to modern geological maps to ascertain the stratigraphic relationships of the area. A similar example in obtaining precise data long after the expedition is seen in the outstanding herbarium from the expedition at the Academy of Natural Sciences in Philadelphia.

Other than Lewis's meticulous collection (most of which survives today), and the respectable sampling of geological materials along the expedition route (most of which have been lost), there were no systematic specimen collections. We purposely overlook the ethnological collections from Native American tribes because while these were purposeful collections they were often a matter of good will with their makers or owners and thus could not be a conscientiously unbiased, scientific collection. We may take note, too, that the soldiers were not "shell collectors," either. In fact, the only seashore collection that we can account for is a specimen of seaweed, from near Fort Clatsop on the Pacific coast. So, based on this slight observation that the party did not collect seashore specimens, similarly whatever fossils might have been collected en route would have been serendipitous—like Sgt. Gass's fossil fish jaw and Clark's possibly dinosaurian "fish rib"—and unnoted in the travelers' journals.

The only documentation that exists for the fossils collected by the expedition is the inventory of the first shipment of specimens from Fort Mandan, received at the American Philosophical Society late in 1805. John Vaughan's register itemizes these specimens, which then were passed along to researchers in various fields of study. As for anything else received after the end of the expedition, there is no record of receipt (although obviously they did arrive). They seem to have been simply passed along to the researchers who had already received some of the treasures of the expedition. If they were indeed duly registered, that record has not been found.

1. John W. Jengo, "'Mineral Productions of Every Kind', Geological Observations in the Lewis and Clark Journals and the Role of Thomas Jefferson and the American Philosophical Society in the Geological Mentoring of Meriwether Lewis," in Robert S. Cox, ed., The Shortest and Most Convenient Route: Lewis and Clark in Context (Philadelphia: American Philosophical Society, 2004) 136-214.

2. Ibid., 189.

3. Storms erode streambanks and open slopes by sheetwash, sometimes exposing fossils in situ—a dependable process eagerly anticipated by fossil hunters. I can personally attest to this, too, having had a weakened cliff face of clay and sand collapse on me (and lived to tell about it). [E.S.].

4. Richard Harlan, "On a New Fossil Genus, of the Order Enalio Sauri, (of Conybeare)," Journal of the Academy of Natural Sciences of Philadelphia, vol. 3 (1824), pp. 331-337, pl. 12.

5. William D. Conybeare, "On the Discovery of an Almost Perfect Skeleton of the Plesiosaurus," Transactions of the Geological Society of London, 2nd series, vol. 2, no. 2 (1824), p. 414.

6. Samuel G. Morton, Synopsis of the Organic Remains of the Cretaceous Group of the United States, Key and Biddle (Philadelphia, 1834), p. 25. Thomas Nuttall was a botanist who was the first scientist to traverse part of the Lewis and Clark trail, the Missouri River, in 1811. U.S. Army Major Stephen Harriman Long commanded an expedition in 1819-1820 to explore the middle Great Plains to the Rocky Mountains. The party included 22 military and scientific men; it was the first of its kind in America.

7. Marl, with etymological roots in Celtic and Latin terminology, is usually a sandy mud rich in calcium carbonate, or lime. It is often found in lake sediments, but in the contexts of this discussion the sediments mentioned here were deposited in quiet marine environments during the Cretaceous Period. The limey composition of loosely consolidated marls, being an easily worked acid-neutralizing product, makes them an excellent fertilizer. The glauconitic strata mentioned here are especially rich marls, containing up to 90 percent of the green mineral, glauconite. The coastal plain in New Jersey in particular had once supported a thriving glauconite marl-mining industry, supplanted in the 20th century by more efficiently produced chemical fertilizers. However, one marl-mining company still operates today in Gloucester Co., NJ; its product is used principally as a water softener.

8. Moulton, Journals, 8:226, 228-9n7. Moulton's note mentions Hadrosaurus and Albertosaurus, but the faunal list is emended here (fide Edward Daeschler, written communication).