Here's a tip for you: When digging for clams, you can tell where they have buried themselves by the discolored patch of sand. But if you dig straight down, you won't find it. Clams dig down at an angle. So you have to dig around the dark spot to get the clam.

I'm not even joking. I've dug clams before, so I know of which it is that I speak.

And speaking of digging things, don't dig up worms. It takes too long. Get a couple of spikes, about a foot in length, and using copper wire, connect them to the terminals of a car battery. Well, stick the spikes into the ground about a foot and a half apart before you connect them to the battery. If the soil is moist, the electricity will drive the worms to the surface where you can pick them up.

And if you even come across a badger hole, don't say to your friends "Do you suppose it's in there?" while sticking your face into the hole. If you do that, the chances are, it will be, and you will be going home without a face. Not because badgers are mean. They really aren't. But they will defend themselves if they feel threatened. And you sticking your face in it's hole is seen as a threat by most badgers. So, don't do it. This advice also rings true when dealing with wolverines.

Also, word of warning, forget how cute otters are. If you see one in the wild, remember they are still wild animals and while they are curious and may appear to be friendly, they will attack if they feel threatened. And any movement towards them can be seen as threatening. An otter might jump up on a dock and sniff out person A's shoes, and even allow that person to touch it. But then when it goes over to person B, it might just bite that leg. So be careful.

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And when you are out in the wild and see a bear and her cubs, don't ever get between me and the escape route because I'll knock your ass down in my haste to escape. I don't need to outrun the bear; I only need to out run you! And If I knock you down, outrunning you becomes easier.

So, why am I giving people tips for dealing with the wild? Because today is the first day of spring! And I'm padding my word count.

But let's move on to today's subject. Today is Friday which means, Friday Rocks! This is the day when I indulge my personal hobby of collecting rocks with dead things in them and inflict them on you.

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For the last few weeks, I have been talking about trilobites. But I thought I'd give everyone a break from the bugs and show something else today. So today, I am showcasing a couple of replacement fossils. These are Cast fossils, meaning they were covered up and then decomposed away leaving an empty mold, as well as replacement fossils, which means all the original material has been replaced by minerals instead of the original material becoming mineralized.

The first example, pictured above, looks like a clam. But it's not a clam. It's some species of bivalve.I'm not an expert on bivalves, but I think it's a species of Tellina and is about 20 million years old. You might notice that it doesn't look like a normal shell you would find. It almost looks like it's made out of Mother of Pearl. But it's not. It's an opal. When the clam died, it was covered with sediment. The sediment hardened around the bivalve, and it rotted away. Then a silica solution in water flowed into the empty cast and hardened. So all that is preserved is the exterior details of the original. Maybe.

If the silica solution seeps in before the internals of the buried creature decomposed, the interior details of the fossil may be preserved. In the case of my bivalve, It would have to be cut open to see which happened. And I'm not doing that. I'm going on averages. Most of the opalized fossils that retain interior structure are bones and wood. So, theres a very good chance, almost none in fact, that there is no interior structure preserved in the above bivalve.

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Opalized fossils aren't actually all that rare. Well preserved ones like my example are rarer than regular opalized fossils are, though. Most fossils that have opalization aren't fully opalized. As a result, many of them are cut by jewelers into regular gemstones. There's a chance that the opal ring or pendant you're looking at once was a tree. Or a brachiopod.

But opal isn't the only mineral that replaces the original when they fossilize. Pyrite is another.

I have 3 different specimens of pyritized fossils. One of them, when I took a picture, you can't tell at all. The pyrite doesn't show in the picture at all. The second, which is the one I'm featuring here today, doesn't really appear to be pyrite either. It looks like it might be shiny, but if you didn't know it was pyrite, you probably couldn't tell. I must stress that, if you saw them in person, there would be no doubt that they are pyrite. Just take my word that if you saw it in person, it would be sparkly and gold-ish. (the third example you can easily tell it's pyrite, but I want to use it in a later post because as well as being pyrite, it has soft tissue preservation.)

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This fossil is a type I don't believe I've shown before. It is an example of a Crinoid. Crinoids are interesting creatures. They look like plants. The can root like plants. They have fronds like plants. But they are animals. The example I have here is mostly fronds. You can see at the top leaf like structure. And in life, that's exactly what they looked like. In fact, Crinoids make up the class Crinoidea, whick comes from the Greek krinoa - 'a lily', and eidos - 'form'. Today they are sometimes referred to as sea lilies.

And if a sea lily is something you could swear you have seen alive in an aquarium, you would be correct. Crinoids still exist. Not the same species that were around millions of years ago, but they are still around. And they have been around for a long time. An example of Echmatocrinus was found in the Cambrian deposits of the Burgess Shale in British Columbia that date back to ~510 million years ago. This is a problematic fossil though. It's either an early crinoid, or an early octocoral. Widespread crinoid fossils don't appear until the Ordovician, about 485 million years ago.

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Anyway, there are still ~600 species of crinoid alive today. But they were once so prolific, many deposits of limestone are made up entirely of crinoid fossils. If you ever get to visit Egypt, take a close look at the limestone blocks that make up the great pyramids. You can still clearly make out individual fossils, including crinoids.

I plan on doing some crinoid posts, (and maybe a couple on echinoderms, the phylum crinoids belong to). I'll probably switch back to trilobite next week, but I might not. I might just give you another break from them and feature something else. I guess we'll just have to wait and see.