I went looking for petrified wood.
Are you interested in rocks?
I love unusual rocks. Before I retired, I used to go out alone to collect minerals and fossils. For the past few years, I could barely go at all, but now that I have retired and have more time, I wanted to start collecting again.
I had been curious about petrified wood — a kind of plant fossil — so I did some research and found out that you can pick some up along the Kakogawa River.
(From the book Stone Field Guide — Not Just Pretty Stones)
When I asked Claude for advice, it told me that the Minō River, part of the Kakogawa river system, would be a good place to look. Apparently, the headwaters flow through the Kobe Formation, where plant fossils have often been found. Since the rock there is tuff, Claude suggested I look for whitish stones.
Because of the rain the day before, the river had risen, and the riverbed was almost completely underwater. I pushed through the undergrowth along the embankment road and made my way down to the riverbed.
I couldn't find the whitish stones I had been told about, so I collected a few brownish ones instead.
Petrified wood? Or just chert? — A siliceous brown stone. If you know what it is, please tell me!
When I got back to the car, I noticed a tiny bug on my clothes. I don't know what it was. I knocked it off. I was glad it wasn't a tick.
There was a low-water bridge there, and this was said to be a spot where traces of petrified wood could be found on the riverbed near it. I could see several holes in the bedrock, each about 20–30 cm across.
When a stone gets trapped inside a hollow, the current spins it around and it slowly drills a round hole into the riverbed.
When the water level drops, those holes become visible at the surface.
Some say these could be potholes, but here they only appear on the upstream side of the bridge — there are none at all on the downstream side of the bedrock. For this reason, they are thought to be the marks left by petrified trees that once stood upright there.
I wonder what kinds of trees stood here long, long ago. It's fun to imagine.
There was something that looked like petrified fallen wood. Could the dark parts be where the wood has carbonized? The brownish parts are also clearly different from the surrounding white bedrock. Normally it would probably be easier to see, but it was submerged because of the high water.
I moved to a different location and had another look. I collected a stone with fine white parallel lines running through it, but when I got home I found it had broken into small pieces, so I realized it was just tuff after all.
I want to study how to identify petrified wood, and then try again.
珪化木を探しに行ってきました。
みなさんは石に興味がありますか？
私は珍しい石が好きで、定年前は一人で鉱物や化石の採集に行っていました。この数年は、ほとんど行けなかったのですが、退職して時間もできて、また採集に行きたくなりました。
気になっていた珪化木（植物の化石）を採集したいと思い調べると、加古川で拾えることがわかりました。
（「きれいなだけじゃない石図鑑」より）
Claude に相談すると、加古川水系の美嚢川がよいという回答でした。源流が神戸層にあり、植物の化石がよく発見されたからだそうです。凝灰岩なので、白っぽい石を探すとよいと提案されました。
昨日の雨で川が増水し、川床がほとんど水没しています。堤防の道から藪漕ぎをして川床に降りました。
教えられた白っぽい石は見当たらなくて、茶褐色の石を数個採集しました。
珪化木？ただのチャート？珪質の茶色い石 見識のある方、教えてください
車に戻ると服に小さな虫が乗っかっていました。何かはわかりません。叩いて落とします。マダニでなくてよかった。
ここには沈下橋があり、その付近の川床に珪化木の痕跡があるという地点です。岩盤に直径20〜30cmほどの穴が数個空いているのがわかりました。
窪みの中に石が入ると水流で石が川床を削り丸い穴になるもの。
水面が低くなるとその穴が地表に出て見られる。
ポットホールという説もあるそうですが、ここでは橋の上流側にしかなく、下流側の岩盤には全くありません。珪化木が立っていた跡と考えられるそうです。大昔、ここにどんな木が立っていたのでしょうか、想像するとおもしろいです。
倒木らしき姿をした珪化木がありました。黒っぽい部分は木が炭化したものでしょうか。茶褐色の部分も白い岩盤の中で明らかに異質です。普段はもっと見やすいのでしょうが、増水のため水没しています。
別の地点に移動して探して見ました。白い筋が平行に細かく入った石を採集しましたが、帰宅してみると細かい破片に割れていたので、ただの凝灰岩だったとわかりました。
珪化木の見分け方を勉強して、再挑戦したいと思います。
Meaning: To gather things — especially natural objects like fossils, minerals, or plants — from the wild. In this article it describes going out to find and bring back rocks and fossils.
→ 「一人で鉱物や化石の採集に行っていました。」
Usage tip: Collect (verb) and collecting (noun/gerund) are both common. "I collect stamps" or "I enjoy collecting stamps."
Meaning: Covered completely under water. In this article the riverbed is submerged because the river has risen from rain.
→ 「川床がほとんど水没しています。」
Usage tip: Submerged is an adjective. The verb is submerge: "The flood submerged the road." You can also say underwater in everyday speech.
Meaning: A sign or mark left behind by something that once existed. In this article, the holes in the bedrock are called traces of trees that once stood there.
→ 「川床に珪化木の痕跡があるという地点。」
Usage tip: Trace is used for both physical marks ("traces of paint") and evidence of the past ("no trace of the building remains"). The verb trace means to follow or find the origin of something.
