I've only managed to get out once in the last week to a local spot that exposes London's "strata" -- And by that I mean the vast depths of glacial overburden when all of this was once Lake London 13,000 years ago before it burst spewing more than five times the force of Niagara Falls, and emptying out in a matter of days. The nearby ski hill, for instance, is not imported riprap, but glacial erratics transported by the force of rushing waters. Anyhow, no real keepers on this visit. The material is a mixed Devonian salad that extends from the Hamilton Group down to the Bois Blanc Formation. These are all Anchiopsis anchiops pygidia from this location. What is interesting is that these appear in three distinct lithologies. I also spent some time between grading papers in the lab. This is a one inch / 2.5 cm baby Isotelus from Bowmanville I picked up about a year and a half ago just in case the urge struck me to do some resto with Milliput. I decided to give it a go. As can be seen, a lot of the trilobite was missing. Since it is very small, and I have big mitts with not the best carving tools, it didn't go as well as I would have liked...But I can actually fix this by smoothing out a few portions (with some fine grit sandpaper and very light abrasion) and ever so slightly downsizing the eyes, which actually turned out the shape I wanted them to be. Okay, what's next? A before and after of a Ceraurus pleurexanthemus I found in the Neuville Formation on my recent trip to Quebec. Both genals, tail spines, and eyes are present. There were some issues with a hard calcitic crust, but I was able to dolomite my troubles away. All that remains is some very careful matrix landscaping to make it pop. The photo does little justice to it, mostly on account of the finished product still being a bit dusty and damp. But here's a more dramatic shot: The cephalon tucks down a bit, but I think it is a pretty decent prone. It is not easy finding these without something missing, like an eye or tail spine... or just finding bits and pieces forever.
It's been a rainy autumn so far, which puts a damper on getting out in the field. So, why not warm up the tools? I started out with one piece with three trilobites on it, a combination flip and stabilization job. The shale is very brittle with numerous hidden fractures... and the pieces were not snug enough for the gluing, and there wasn't much of a way of fastening them together with the vice clamps without breaking the shale. Suffice it to say, it was an unmitigated disaster... but one I can fix later when I have the patience to give it another go. It wasn't the best of my ideas to take on a complex job right away! I am performing a flip job on a ventral, and waiting for the matrix-paste I ground up to cure. That I'll save for another post. Let's get to the low hanging fruit. This is a Gravicalymene sp. I found in the Nicolet Fm in the Montreal area. Sadly, it was already exposed and missing some shell. Still, I made the best of it. I could tinker with it a bit more, of course. This is soft shale that takes well to baking soda abrasion. I didn't once have to take out the scribe for this one. This is a giant, inflated Eldredgeops rana that I found not far from my house, in a particular horizon of the Dundee Fm that is cherty and breaks in chunks -- many times right through fossils. My collecting friend and expert preparator advised me to be very careful with this one since, well, how many Dundee Fm Eldredgeops rana have people found? Unlike the same species in the Windom shales of Penn Dixie, this one is not small or partially flattened. But, as can be seen, it is missing some shell and requires a bit of resto. Preparation in this rock is hardly simple. This specimen needed considerable stabilization even before even thinking about scribing. I used the ME-9100 to remove the big chunks of matrix, always careful to control any transferred vibration that would cause the rock to break apart in an inconvenient spot. I swapped between a Pferd and full dolomite abrasion for the rest. This was a tricky bug, including some fractured mess at the top of the glabella, and the shell is both relatively thick but also very fragile.. Still, a plump and healthy specimen measuring 50 mm (2 inches), or 60 mm (2.5 inches) if completely outstretched.
It would look even better if I landscape the matrix more, but I can't seem to master that skill yet. This weekend I was able to get back to my Dundee Formation spot in Oxford County. The site is not quite perfect to permit full access yet, but in a few weeks (and early spring) will open up more of the rocks. It should be stated that these are brutally hard rocks that will shatter -- or the bones of the person who hammers these may shatter! This is why part of the excursion requires selecting the right rocks where natural forces have made them slightly more fissile for splitting. The fossils generally appear silicified, much akin to the Amherstburg Fm material I also collect from. Nothing amazing, but it was an interesting visit. I have already shown what the matrix is like in a post back in April, so I'll just show some of the things I picked up. Brachiopods are, by far, the most conspicuous and numerous fossils to be found in the platy layers, followed by abundant rostroconchs. Not only that, but the brachiopods could attain very plump and robust sizes as pictured above. There is an incredible diversity of them unmatched in most Devonian strata in Ontario. The brachiopod on the lower left is quite a looker, full detailed, free of matrix and with both valves. A calcified gastropod that looked sparkly in the sun at the upper left. And, of course, obligatory rostroconchs that I would put in my pocket if they came free of the matrix. I did keep one in matrix with a buddy brachiopod to function as an association piece should I donate a number of these to a museum. On to the trilobites. Most of the species in this horizon were encountered, including countless Pseudodechenella sp. parts I tend to pass over. I do make an exception for these Odontocephalus sp. given that they are very likely a new species, which means collecting as many samples as possible. They were not as numerous today, and there were some fragments of denticle cephalic margin I didn't bother collecting, as well as some pygidia that were too busted to be of much use. Instead, my goal was to collect fragments that had much clearer diagnostic details, and particularly the morphological trait that would assist in describing this as a new species: the forked pygidial spine. Compared to previous visits, the giant dalmanitid, Coronura aspectans, was particularly abundant -- in fragments only, of course. In most cases it would be the presence of a single thoracic segment. The piece with the most promise would be the one on the bottom where a good portion is buried in the matrix and awaiting my prep tools. The photos do no justice to these partials. This again is a Coronura pygidium, much of it buried in both the positive and impression side. Some prep will be needed.
In all, a fair outing. The deposition conditions were turbulent, which rarely ever bodes well for finding complete trilobites, but it is a possibility. I am fairly confident that it is just a matter of time and repeat visits that I may come upon a complete one. A complete Coronura would be an incredible coup, but a full Odontocephalus would be invaluable to science. Yesterday was a perfect day to be out. Not only was it national fossil day (at least in the US, but I suppose we can extend that more internationally), but it was in mid-teens, and a good mix of sun and cloud. I made my way to the local Amherstburg/Lucas Fm spot with no real expectation of finding much of anything at all given that I've made so many visits as to deplete its more gainful rocks. I can't say that this trip provided me with glorious finds, but it was a fair outing. I neglected to take a picture of the armour stone I was dealing with. Let us just say that it was big, heavy, and very dense. How dense? I had scored the sides at multiple locations for getting in the chisel, which I was able to sink by a good two inches at each spot without so much as causing a crack -- just tons of rock powder. But, with a couple hundred more blows moving from hole to hole, a hairline crack emerged, and another hundred blows split the beast in two. It is simply the stubborn nature of many Devonian rock formations in Ontario to be brutally hard, with a tendency to shatter rather than split, which makes collecting specimens an added challenge.
Occasionally, these long bryozoans appear, and nearly all of the representatives of this species are mineral stained a deep ochre. I found a few poorly preserved pygidium fragments of Acanthopyge contusa. Due to the silicification, the negative (on the right) are far clearer than the positive to show diagnostic details. More of the same. Pseudodechenlla sp. parts are widespread throughout the "layers," including isolated cheeks and pygidia. I suspect this may be one of the poorer examples, or possibly a Trypaulites. On the right is a partially buried Crassiproetus in a typically busy hash. Thoracic segments are not entirely common in this material, as it seems to favour fragments of cephalons and generally complete pygidia. The size and width of these segments suggests Crassiproetus crassimarginatus. The pair on the right -- "fat man and little boy" -- are also the same species. The two rarest to be found include a pygidium of Mystrocephala stummi, and a partially buried and poorly preserved Echinolichas sp. At this point, I probably have about six examples of this incredibly rare lichid not reported in Ontario rocks.
It would be a fool's errand to assume complete trilobites will ever be found in this material given the depositional conditions, and so one must be content with fragments. It is an interesting lithology which also gives off a kind of petroliferous odour. Unless I start flipping more rocks in the pile at random in the hopes of locating more rocks of this specific horizon, I may have tapped this location out. It has been since late August of 2019 that I have made repeated visits here, and I have performed due diligence in collecting almost every lichid fragment and most intact rare species fragments (Mystrocephala, Trypaulites), if not a few almost complete Pseudodechenella and plump Crassiproetus pygidia. Many of these will likely form part of a museum donation at some point. This was a nice way to spend national fossil day. Although the finds were not showstoppers, I can be content that I bumped into examples of just about every species that can be found in this material, and they all emerged from one single armour stone that took a number of hours to break down. |
Kane Faucher
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February 2024
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