“E” is for “Entrance” and “F” is for “Fossil Worm Casts”

A Facebook Group I belong to, “New Zealand Lapidary, Rocks, Minerals, Fossils”, invited its members to submit photos each week of a stone, mineral or fossil in their collection that starts with a letter of the alphabet. My Posts for “A” and “B” can be found here. The following are my Posts for “E” and “F”.

“E” is for “Entrance” – This is the opposite of “Eye”. An “eye” in a stone “looks outwards” and is often opaque. An “entrance” allows you to “look into” a stone, to see beyond its surface. “Entrances” can be translucent veins or crystals or druzies or holes or cracks. This tumble-polished stone, 6.5 cms long and 3.5 cms wide, comes from a Kakanui beach. There are many small clear “entrances” to it, maybe vesicles filled over time as water moved through them. Your eye is drawn to look inside the stone.

“F” is for “Fossil Worm Casts” – This is the term used locally for trace fossil stones found at Gemstone Beach in Southland (I have also found the same stones elsewhere in Southland and around Whanganui). I found this stone on Gemstone Beach in February this year. A no-longer-in-place Heritage Trail sign refers to these stones as “Fossil Worm Casts”. The Riverton Museum Te Hikoi has a couple on display, labelled “Worm Trace Fossils”. Te Ara, The Encyclopedia of NZ refers to a “worm-like impression…, traces left by a worm burrowing through mud”.

A geologist I consulted said that these trace fossils were most likely left in argillite rock over 250 million years ago, in the Permian Era, by an animal burrowing within the ancient sea floor. There is a great diversity of trace shapes to be found in these stones, along with variations in size and colour. But you can see how similar they often are to contemporary earthworms and their casts. However, the animals that left these traces could have been quite different. Furthermore, the traces could be “casts” of animals that have dissolved during the petrification process, their bodies being replaced by other material. Which would mean they are not trace fossils… Continued thought and research are required.

For the next Post in this Alphabetical Series, see here. The Series Index is here.