Charles Doolittle Walcott

Mystery at Pioche, Nevada
by

Linda B. McCollum and Michael B. McCollum

Eastern Washington University

When we began our comprehensive study of the Middle Cambrian trilobite faunas of the Pioche Shale in 1993, we realized that the type species of two very important groups of trilobites; the kochaspids and oryctocephalids, had been described from the Pioche Shale by Walcott (1886). We searched the literature for any clue as to exactly where and at what horizon these type species [Kochaspis liliana (Walcott) and Oryctocephalus primus Walcott] had been found. Below is a brief summary of the database, both published and unpublished, which led us (faculty and undergraduates alike) to track down the lost locality.

The first Cambrian trilobites to be found from the Pioche Mining district were in 1871 by geologists of the Wheeler Survey (Gilbert, 1875). A much larger collection of Cambrian faunas from this area was made by Charles Doolittle Walcott (1850-1927) over a three day period beginning on September 21, 1885 and the trip is mentioned by Yochelson (1998, p. 184) in his biography of Walcott. It was to be Walcott's only trip to this area, so one could deduce from this that he was not overly impressed with the results of his visit. The following is a transcription of that trip taken from Walcott's diary and field notebook beginning on September 20, 1885.

Walcott's diary from September 20-23, 1885:
Sept. 20. Camp moved to Pioche. Took dinner there and wrote letters p.m. Telegraphed to chief clerk, USGS relative to meeting director at Kanab, Utah.
Sept. 21. Collecting Cambrian fossils with J.E.W. (J. Edward Whitfield) on the dump of the Chisholm Mine N.W. of Pioche Mine. Good access.
Sept. 22. Rode to Bristol and back 44 miles. Saw section below Eureka quartzite that gained little. Jack very lame on return.
Sept. 23. Collecting fossils about Pioche with J.E.W. Through with work in the region.

Walcott's field notebook from September 20-23, 1885:

9-22-85. North of the main peak of the Highland Range, the strata breaks over towards Stampede Gap and then extends in a long high ridge to the pass a little north of Bristol. At the pass, the light colored Eureka Quartzite caps the ridge on the north side and also the hills on the N.W. side. Estimating the thickness of the strata that is above the horizon of the upper beds of the Highland Peak section. I think 2500 feet is a conservative account.

9-23-85. The Olenellus horizon at Pioche (illegible word) limestone with numerous fossils Ptychoparia etc. The upper layers of the quartzite are a little calcareous in spots and these contain numerous fossils. [This collection was later referred to as USNM locality 31a].

Walcott's measured Cambrian section in the Highland Range from undated notes:

Cambrian section of the Highland Range on the west side half way between Bennett's Spring to Stampede Gap. The base of the section begins at the Quaternary and the western slope and the summit forms the apex of the range.

Walcott's published reports:

Walcott (1886, p. 33-35) published the Highland Range measured section and described the Cambrian faunas he'd collected from the Pioche district. The "Walcott Mystery" begins with this publication and centers on the stratigraphic horizon of the fossils he collected on September 23, 1885 from the calcareous "spots" in the quartzites. Walcott (1886, p.35) writes "On the east side of the anticlinal arch at Pioche, 20 miles east of the Highland section, the strata resting on the quartzite (2, 3 and 4 of section) contain the following species, four of which are found in the two localities:"

Of the eleven species he lists, only four are trilobites: "Olenellus Gilberti" Meek 1874, "Olenoides levis" n. sp., "Crepicephalus Augusta" n. sp., "Crepicephalus Liliana" n. sp., and he correlates both the faunas and lithology of this locality back into his Highland section. In addition, Walcott (1886, p.210-211) describes a new genus and species, Oryctocephalus primus, "In limestone just above the quartzite, east of Pioche, Nevada". Walcott (1886, p.187) noted that "Olenoides levis" occurs with "Olenellus Gilberti" and that the Lower Cambrian was defined by Walcott (1891) to be the range zone of Olenellus. Thus, all five trilobite species listed above were considered by Walcott to be lower Cambrian forms, but remember that three of these species were new to science and had never been found before.

Although Walcott spent only a few days collecting in the Pioche Mining district, he referred back to his measured section in the Highland Range and revised his faunal lists. In 1908, Walcott named the Pioche Shale and later, in 1916, named the Chisholm Shale. Walcott (1912) gives a somewhat better location for this Highland Range measured section, as "8 miles north of Bennett Spring" and gives two revised Lower Cambrian faunal lists. From locality 30, which is the Highland Range section, he lists the following trilobites: Callavia nevadensis Walcott [now Olenellus], Olenellus fremonti Walcott, Olenellus gilberti (Meek), Peachella iddingsi Walcott, Crepicephalus augusta Walcott, and Crepicephalus liliana Walcott. From locality 31a, which is southeast of Pioche along the road to Panaca, he lists the following trilobites: Olenellus gilberti (Meek), Oryctocephalus primus Walcott, Zacanthoides [was "Olenoides" in 1886] levis (Walcott), Crepicephalus augusta Walcott, Crepicephalus liliana Walcott, and Ptychoparia sp. The only other person to publish on the Cambrian rocks of the Pioche district during Walcott's lifetime was Fred J. Pack (1906a,b), but his faunas came from higher in the section, mostly from the Chisholm Shale.

Published reports after Walcott's death in 1927:

The first systematic study of the regional geology in the Pioche region began by USGS geologists in 1922 and continued until 1926, gave the first graphic representation of the aerial extent of the Pioche Shale in the type area (Westgate and Knopf, 1932). Besides the geologic map of the area, they named the Lyndon Limestone, which separated the Pioche Shale from the overlying Chisholm Shale. Although they relied heavily on Walcott's published reports, they did present a graphic section of the Pioche Shale (fig. 4) from a section on a ridge north of Lyndon Gulch, on the west side of the Highland Range.

After Walcott’s death, Charles E. Resser began a systematic redescription of the Cambrian trilobite collections housed in the Smithsonian Institution. Resser (1935, p.36) erected a new genus, Kochaspis, and placed many of Walcott’s Crepicephalus species into it, including the Pioche Shale species: K. liliana (Walcott) and K. augusta (Walcott). Resser (1935, p.37) proposed two new species, K. nevadensis and K. highlandensis for the Pioche specimens Walcott had collected in the Highland Range. Resser still considered these species to be Lower Cambrian.

Mason (in Grabau, 1936) appears to be the first person to realize that the Pioche Shale Kochaspis species were younger and occurred above the Lower Cambrian Olenellus Zone faunas. Until then, all of the Pioche Shale was considered Lower Cambrian in age. Mason proposed that the Lower Cambrian portion retain the name Pioche Shale while the Middle Cambrian receives two new shale formation names; the Forlorn Hope Shale and the overlying Comet Shale.

Charles Deiss began measuring numerous Cambrian sections and collecting Cambrian faunas from the western US in 1931 and included a section in the Highland Range (Deiss 1938, p.1149-1161). Deiss assumed that Walcott had measured his section in the vicinity of Lyndon Gulch, as Westgate and Knopf (1932, p. 9-10) had noted that the best exposed and least faulted section of the Pioche Shale in the Highland Range occurs there. Deiss (1938) also restricted the term Pioche Shale to the 183 meters of strata thought to be Lower Cambrian, but the 113 meter thick Middle Cambrian portion was assigned only to the Comet Shale. The base of the Comet Shale was defined on the 4 foot thick oolitic and oncolitic limestone containing Kochaspis augusta (Walcott). One thing to note in Deiss’s measured section is that the highest occurrence of the Lower Cambrian genus Olenellus is 100 meters below the basal Middle Cambrian Kochaspis augusta (Walcott) fauna. This interval between the Olenellus Zone and the Kochaspis liliana Zone became the Syspacephalus Zone in the Howell et al (1944) Cambrian correlation chart of North American.

Harry E. Wheeler also began a study of the Cambrian formations in the Great Basin and published two papers on the Pioche district (Wheeler and Lemmon, 1939, and Wheeler, 1940). Wheeler and Lemmon (1939) firmly believed that there is no justification for designating formations purely on faunal grounds and rejected the idea that Walcott’s Pioche Shale should be divided into one or more formations. Their view persists to this day.

Franco Rasetti (1951, p.225) commented briefly on Kochaspis liliana (Walcott) from the Pioche Shale and noted that the only associated species that occurs on the rock is Oryctocephalus primus Walcott. Rasetti (1951, p.84-93) discusses at length the inconsistent placement of the Lower-Middle Cambrian boundary in terms of faunas and argues that the boundary be placed at the top of the Olenellus Zone. He also proposes two new basal Middle Cambrian zones for his sections in the southern Canadian Rocky Mountains; the Wenkchemnia-Stephenaspis Zone and the overlying Plagiura-Kochaspis Zone.

A.R. “Pete” Palmer made an appraisal of the Great Basin Middle Cambrian trilobites described before 1900 and this included Oryctocephalus primus Walcott, Kochaspis augusta (Walcott), and Kochaspis liliana (Walcott) from the Pioche Shale (Palmer, 1954). Pete did not include any of these three species in his discussion of the Pioche Shale faunas in Merriam (1964) because their stratigraphic position and precise locality was still unknown. Merriam (1964) did provide a much needed discussion of the Cambrian section in the Pioche mining district.

The Walcott Mystery Revealed

Almost 120 years have now passed since Walcott spent a peaceful day, September 23, 1885, collecting trilobites southeast of Pioche along the Panaca road. He must have collected from more than one site, but decided that all of that day’s collections were from essentially the same stratigraphic horizon based on the presence of Olenellus gilberti and the quartzite horizon in his measured section made the previous day in the Highland Range. It would be 50 years before anyone realized that his faunal list was composed of taxa that came from at least two different horizons. It had been over a hundred years and nobody had relocated or recollected the faunas Walcott found along the old Pioche-Panaca road.

The first thing was to find a map showing the location of the old Pioche to Panaca roadbed since the present state highway had been relocated several times over the past century. We obtained a USGS topographic map at a scale of 1:100,000 dated 1885 and a 1:62,500 scale map dated 1916, both showing the location of the old Pioche-Panaca road. We compared the road’s location to the most recent 1:24,000 scale topographic map dated 1953 and photorevised 1969 and found that the old paved highway leading southwest from Pioche follows the same grade till it intersect US 93 about a mile and a half out of town. The trace of the old roadbed can be found above the roadcut at the southern junction of old US 93 and the newer bypass. The old roadbed continues in a southward direction one canyon to the east of the present highway.

In the Spring of 1994, using a 1:12,000 scale geologic map (Park, Gemmill, and Tschanz, 1958), the students and I retraced Walcott’s day trip on foot from just west of the highway intersection between Red Hill and Gray Cone southward for over a mile. We located Albertella Zone faunas in the old road bed and found olenelloids in both the Delamar Shale Member and in the Combined Metals Member along the sides of the road. We even found a great place to collect faunas from the Susan Duster Limestone Member just to the east of the old Panaca road. We did find quartz sandstones with calcareous horizons along the low ridge separating the old road from US 93 just south of the junction, but only a few trilobite fragments were found.

It was getting near the end of the day and hope was flagging. As we walked northward along the sandstone ridge toward the roadcut at the intersection, one of the students broke open a fossiliferous limey layer in a chunk of sandstone which was part of the road metal along the highway. Within a few minutes, everyone was breaking up pieces of limy sandstone and numerous specimens of oryctocephalids and kochaspids were being found. The source of the material was easily traced back to a sandstone unit at the top of the Log Cabin Member which was well exposed in the roadcut.

The relocation of Walcott’s kochaspid fauna, plus additional collections from several new localities from the same horizon, revealed a rather diverse fauna including 9 genera and species. Fred and I have presented revised descriptions of Walcott’s three species; Oryctocephalus primus Walcott in Sundberg and McCollum (1997), Kochaspis liliana (Walcott) in Sundberg and McCollum (2003), and reassigned Kochaspis augusta (Walcott) to Kochiella in Sundberg and McCollum (2002). The other 6 genera and species, which include one new genus and four new species, are described in Sundberg and McCollum (2003).

One other point, if you’re interested in biozonation, is that the first occurrence of the genus Plagiura in the Pioche Shale is within the Kochiella augusta assemblage of Sundberg and McCollum (2003). Thus, the Plagiura Zone of Deiss (1939), the Kochaspis liliana Zone of Howell et al (1944) and the Plagiura-Kochaspis Zone of Rasetti (1951) all have the same FAD. The FAD of Poliella occurs at a much lower stratigraphic level, there Sundberg and McCollum (2003) chose the oldest species of that genus, P. denticulata, to name the biozone formerly referred to as the Plagiura-Poliella Zone.

REFERENCES

Deiss, C., 1938, Cambrian formations and sections in part of Cordilleran trough. Geological Society of America Bulletin, v. 49, p. 1067-1168.

Deiss, C., 1939, Cambrian formations of southwestern Alberta and southeastern British Columbia. Geological Society of America Bulletin, v. 50, p. 951-1026.

Grabau, A.W., 1936, Paleozoic formation in the light of the Pulsation theory, v. 1, Lower and Middle Cambrian pulsations, Second edition, p. 257-295.University Press, National University of Peking.

Howell, H.F., Bridge, J., Deiss, C.F., Edwards, I., Lochman, C., Raasch, G.O., Resser, C.E., Duncan, D.C., Mason, J.F., and Denson, N.M., 1944, Correlation of the Cambrian formations of North America. Geological Society of America Bulletin, v. 55, p. 993-1003.

Merriam, C.W., 1964, Cambrian rocks of the Pioche Mining District, Nevada. U.S. Geological Survey Professional Paper 469, 59 p.

Pack, F.J., 1906a, Geology of Pioche, Nevada and vicinity. Columbia University, School of Mines Quarterly, v. 27, p. 285-312, 365-386.

Pack, F.J., 1906b, Cambrian fossils from the Pioche Mountains, Nevada. Journal of Geology, v. 14, p. 290-302.

Palmer, A.R., 1954, An appraisal of the Great Basin Middle Cambrian trilobites described before 1900.U.S. Geological Survey Professional Paper 264-D, p. 55-86.

Park, C.F., Jr., Gemmill, P., and Tschanz, C.M., 1958, Geologic map and sections of the Pioche Hills, Lincoln County, Nevada. U.S. Geological Survey Mineral Investigations Field Studies Map MF-136.

Rasetti, F., 1951, Middle Cambrian stratigraphy and faunas of the Canadian Rocky Mountains. Smithsonian Miscellaneous Collections, v. 116, no. 5, 277 p.

Resser, C.E., 1935, Nomenclature of some Cambrian trilobites. Smithsonian Miscellaneous Collections, v. 93, no. 5, p. 1-46.

Sundberg, F.A., and McCollum, L.B., 1997, Oryctocephalids (Corynexochida: Trilobita) of the Lower-Middle Cambrian boundary interval from California and Nevada. Journal of Paleontology, v. 71, p. 1065-1090.

Sundberg, F.A., and McCollum, L.B., 2002, Kochiella Poulsen, 1927, and Hadrocephalites new genus (Trilobita: Ptychopariida) from the early Middle Cambrian of western North America. Journal of Paleontology, v. 76, p. 76-94.

Sundberg, F.A., and McCollum, L.B., 2003, Trilobites of the lower Middle Cambrian Poliella denticulata Biozone (New) of southeastern Nevada. Journal of Paleontology, v. 77, p.331-359.

Walcott, C.D., 1886, Second contribution to the studies on the Cambrian faunas of North America. U.S. Geological Survey Bulletin 30, 369 p.

Walcott, C.D., 1891, Correlation papers; Cambrian. U.S. Geological Survey Bulletin 81, p. 317.

Walcott, C.D., 1912, Cambrian Brachiopoda. U.S. Geological Survey Monograph 51, Part I, 872 p.

Westgate, L.G., and Knopf, A., 1927, Geology of Pioche, Nevada, and vicinity. American Institute of Mining and Metallurgical Engineers Transactions, v. 75, p. 816-836.

Wheeler, H.E., 1940, Revisions in the stratigraphy of the Pioche district, Nevada. University of Nevada Bulletin, v. 34, no. 8 (Geology and Mining series no. 34), 42 p.

Wheeler, H.E., and Lemmon, D.M., 1939, Cambrian formations of the Eureka and Pioche districts, Nevada. University of Nevada Bulletin, v. 33, no. 8 (Geology and Mining Series no. 31), 60 p.

Yochelson, E.L., 1998, Charles Doolittle Walcott, Paleontologist. The Kent State University Press, 510 p.

Last updated 2/04

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