Canadian Rockhound: Some West Coast Crinoid Fossils

Some 22.5 kilometers southeast of Chilliwack, British Columbia, can be found the 7,970-foot high Slesse Mountain. At the base of the mountain's west flank passes Slesse Creek, flowing north into Canada from the United States.

Crinoid columnal
Figure 1. Soaked in hydrochloric acid, the white calcite walls of this crinoid column have been eaten away to reveal the detailed ribbed pattern of the axial canal. The length is 3.5 cm. Photo by P. Thorne.

The creek, a small river in its own right, empties into the Chilliwack River, which in turn empties into the Fraser River. On the creek's short journey of about 12 kilometers through Canada to the Chilliwack River it passes through some of the oldest fossil-bearing rock in this corner of the province.

These are Permian limestones formed 230 or more million years ago. All are of marine origin. The limestone belongs to the Chilliwack formation. A variety of marine fossils have been found in other and related limestones along the American-Canadian border and on the American side, limestone quarries have been in operation for many years. These limestones have produced branching corals, brachiopods (lamp shells) and other invertebrate marine fossils. At Slesse Creek the leading fossils are stems of sea lilies or crinoids. These are most often found in float; i.e., boulders in tributary creek beds.

The limestone is a dark grey and impure. It could just as easily be thought of as a highly calcareous mudstone. When dissolved in hydrochloric acid there is considerable residue left not affected by the acid. It is because of this the acid will react faster with the purer white calcitic material of the sea lily stalk sections (columnals) and leave behind the shape of the columnal's interior (Figures 1 and 2); the former cavity of the axial canal.

Crinoid boulder
Figure 2. A dark grey crinoid limestone boulder cut with calcite veins. The ring-shaped crinoid columns are seen mostly in cross section. This boulder has been polished to enhance the fossils. Photo by P. Thorne.

Figure 3. A collection of crinoid plate sections poorly sorted by water action. From the longitudinal cross-section of a columnal (center bottom) little evidence of distortion from pressure is apparent in the rock although some recrystalization has occurred. A penny indicates the scale. Photo by P. Thorne.

Recrystalization of the calcite has occurred (Figure 3), and fossil crinoid columnals can be found neatly cut in half by white veins of calcite that formed after fossilization. The rock and fossils can be polished to a high gloss to make good display pieces.

The country here is extremely mountainous, rugged and densely forested; all of which makes finding the parent outcrops of these boulders a less than easy task. One such tributary creek with crinoidal boulders is the most northwest stream flowing into Slesse Creek. This one is easy to reach, being only a short walk from the main road on the south side.

The crinoids are something of a mystery. No crinoid heads have been found. The head, or calyx, is used to identify crinoids. The calyx contains the animal's mouth and stomach. As this important part of the animal is missing, identification can only be made on the columnals, which is an uncertain business in this case. Only broad classification can be made.

The columnals are quite large by local standards, an inch or more across. Crinoid columnals found on Vancouver Island are much smaller.

Crinoid
Figure 4. This crinoid stem measures 1 inch in diameter by 11 inches long. Photo courtesy of John Ratcliffe.

Crinoids belong to the Phylum Echinodermata making them relatives of starfish and sea urchins. Crinoidea is the Class name of sea lilies. In examining the crinoids from a selection of boulders it can be seen the Slesse Creek columnals are largely unsorted, indicating little current or wave action while they lay on the sea floor after death. A few boulders with some sorting (with the columnals aligned to one another) probably represent fossils from a higher or lower section of the original outcrop.

Crinoid section
Figure 5. Cross section of a crinoid stem showing axial canal. Photo courtesy of John Ratcliffe.

Crinoid side
Figure 6. Ribbed pattern of a crinoid. Photo courtesy of John Ratcliffe.

In life the columnals are held together with connective tissue. Specimens with 3 or 4 columnals still in a row are found, but from the scattering of plates these animals had been dead for some time prior to burial and fossilization. Decomposition had set in and quite literally has left only the barest of bones. (There is no muscle in crinoid columns so there would be none to fossilize.)

Running through the center of the columnals is the axial canal (Figure 5), making the columnal ring-shaped in cross section. Through this axial canal ran the axial cord.

Also missing from the crinoid remains are holdfasts, the "roots"; the part that held the crinoid to the sea floor or whatever it used as an anchor. This would be as interesting to find as its calyx. The length of the column in life is unknown. Crinoid stem lengths vary from species to species; from a nub up to 21 meters (70 feet) in one fossil from. There are some modern species that are free swimming.

Intermixed with the large columnals are much smaller ones. These probably represent the same species, as crinoids are communal, In fact are often referred to as growing in gardens.

From the number of plates forming the skeleton of a crinoid, including the calyx, arms and holdfast, it may only be a matter of time before sufficient discoveries and research gives a positive identification to these mystery crinoids from Slesse Creek.

Acknowledgements:

The Canadian Rockhound is grateful to John Ratcliffe for contributing the photographs in Figures 4, 5 and 6.

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The preceding article was first published in the Spring 1990 issue (Vol. 2, No. 6), of Cab & Crystal. Reprinted in the Canadian Rockhound with permission.