today i'm working on my geocaching logs from last may's visit to maine, which includes some very interesting earthcaches, which in the best form are lovely little self-guided geology lessons.
there's one about the jim pond formation's basltic lava pillows and right now i'm working on writing up my interpretation of a little jobber about the west brach formation and its ordovician era volcanism.
|yep, there's a vent.|
but no. i can't do that. instead i have to go to the site and take dozens of pictures of the rocks and then come home and later look up maps and articles which are mostly written by geologists for geologists so then i have to look up a lot of terms and i usually end up reading until my brain goes all hurty and then i sleep on it and wake up in the morning and start reading again and it all sort of makes sense.
i found a really AWESOME map of this particular formation that you can see here that explains what was going on here in the early paleozoic eras, which sets you up for having a clue about the devonian eruption of the katahdin pluton.
and if you are going "huh?" i'm only just learning too because before i started reading all this stuff i had a pretty firm grasp of the concept of ordovician shales and devonian shales being separated by silurian limestones, but no real concept of how that fit into any larger scheme.
here's the link to the wikipedia article on geological eras, and there's a handy diagram a little bit down the page.
last week i spent a day over at the paleontological research institute's museum of the earth and later on i will tell you about that.
meantime, i'm just going to tell you that in both the ordovician eras and the devonian eras the conditions on the planet yielded a lot of dark basaltic rocks in which are preserved a lot of fossils. during the silurian era a lot of critters with shells died off and their bodies formed a limestone layer that typically sits between the ordovician and devonian basalts, but sometimes the only way geologists and paleontologists can know which era the basalt belongs to is to date it by the fossil record, which is what they're trying to do with the older rock at the bottom of the west branch formation.
these days mount katahdin is what's left of the katahdin pluton, which apparently is what happened when a large granitic flow pushed upward under the surface of a receding plate.
but here's the really mind blowing thing: we don't get a good grasp of it because we are tiny little creatures moving at hyperspeeds over land that appears to us to be standing still. we look at these formations and talk of eruptions here and plate crashings there but we have, i think, most of us, little appreciation for the fact that the ground where we are standing to look at this stuff ISN'T WHERE IT WAS WHEN IT HAPPENED.
all this stuff didn't happen in maine; what later became maine was then somewhere just north of the equator and moving at a rate of about a centimeter a year toward its present location. it is still moving. later on it is going to crash back into europe again, but we won't be here to see it.