March 4th, 2026
I have two more weird rocks to describe.
Bubble Rock
As described in the main page of this section, the rocks on my land are all metamorphized igneous rocks. They all have strong cleavage planes with angular shapes, are quite hard, and slightly greenish. But a few weeks ago, whilst digging past some of these rocks, I came across one rock a good 8” below the surface that just didn’t fit the pattern:
It is NOT angular, it shows no cleavage planes, and its surface pattern is unlike that of the other rocks. It is 21cm long, 14cm wide, and 9cm high. I ground one edge flat and then polished it smooth; it shows no crystallization.
My guess is that there was a bubble in the original frozen lava. When the material was subducted, something flowed into the bubble. Perhaps seawater flowed into the bubble and brought in minerals that, after a long time, solidified. I think that it’s more likely that, when the rocks were subject to sufficiently high temperatures and pressures, some material more plastic than the surrounding rock was more mobile and was squeezed into the bubble. A chemical analysis of this rock, compared with the surrounding rock, might confirm or reject my guess.
Sandstone among metamorphic rocks???????
My second weird rock is actually a collection of rocks. I mentioned a piece of sandstone in the previous page. It was so out of place that I never gave it much thought; it was just as likely to have been put there as a practical joke by extraterrestrial visitors as to be native to the local geology.
But over the last few days, as I have been working in the forest, I have uncovered a great many pieces of sandstone, including some quite large ones. There is definitely something strange here. Here’s the most striking piece:
1: Diagonal
2. Top
3. Side
4. Close-up of top
Here’s a closeup I obtained of the bottom surface by cobbling together an iPhone with a telescope eyepiece and some strong side lighting. I know, I know, I should get a proper dissection microscope. There are small crystals of quartz mixed into the mass.
Its dimensions are 20cm long, 10cm wide, 5cm high. This piece astounds me. First, its cleavage screams ‘Sedimentary!’ But it’s so thick! You don’t get thick slabs of sandstone like this forming in ponds; this is from a big lake or perhaps even the ocean. But this location has NEVER been coastal.
At this point it is incumbent upon me to address the apparent answer: that this rock was brought here by people. The history of this location just doesn’t support that hypothesis, likely as it may otherwise seem. Here’s a topo map of the area next to a cadastral map of the same area from 1910:
The rock was found at the red X. Note that this is half a mile from the nearest road. Local lore says that there were no habitations in this area until after World War II, and there have never been any on the hill above. The only times that people have been on this hill were for logging operations. I have never found anything on that hillside suggesting earlier habitation. Moreover, I have collected more sandstone rocks in that general area, scattered across an area at least 50 meters long.I therefore discard the hypothesis that this rock was brought here by people.
Note also the peculiar top surface of this rock, shown as image #4 in the image above. Here’s a closeup:
I had to take this shot from a steep angle to make the upper plane more apparent. It’s as if a bunch of grains were scattered across the original flat surface on top and then something big and flat pressed them down. I cannot imagine the process that generated this result.
I am at a loss to explain this rock. The only remotely plausible hypothesis I can imagine is that this rock really came from a sandy beach on a volcanic island off the coast of North America 250 million years ago. The area was subducted and driven deep down, where most of it was metamorphosed into the rocks common to my area. But a small sliver of the topmost material — the beach sand — peeled off from the main body and descended a short distance where it underwent enough pressure to weld it into sandstone, but not enough to metamorphopse it. As the land eroded away over millions of years, it came to the surface, but was covered over by some peculiar event; perhaps an avalanche, perhaps a river whose course suddenly changed in a flood. So it remained covered while the land all around it continued to erode away, until it found itself just above the older metamorphosed rock, and then I stumbled upon it.
This hypothesis is hard to swallow, I’m sure. I hope that I’m in the right ball park, but have gotten some of the details mixed up or out of order. I would very much appreciate any critiques, and would especially appreciate a better hypothesis. I’ll be happy to provide any further details. Here’s my email address in a form that might be less vulnerable to spiders:
