Ledger Stone - Bedrock Granite

Hi, I'm Tim Carter, Ask the Builder. I'm here in center New Hampshire, right on my own street

They're getting ready to build a new home. And you can see how they've scraped. They got rid of all

the trees, a lot of trees here. This is where the house is going to go. They're going to have to do

a lot of blasting. There's a lot of, they're right here. They're into the ledge. And that's what this

video is about, ledge. I want to show you what ledge is. If you've ever watched the old Cary

Grant movie, Mr. Blanding's Builds His New Home. It's a really, really funny part about 45 minutes

into the video. But right here, I'll try to point my finger. This is solid bedrock that, you know

that continues down through the earth. Once you get into the mantle, it's pretty plastic. It's like

taffy. But that is the Meredith porphyritic granite. And there's more of it. It's all over

the place but this is actually an exposed part of the bedrock and you can see the soil there was a

little bit of soil on it right here maybe a couple inches thick but um that's solid bedrock so when

you go to buy a lot a building lot in new england you better be paying attention you better understand

what the bedrock geology is i do phone coaching so if you need help with it my college degree i'm a

geologist but this is a really great example i'll actually walk up to it um so you can get a little

bit closer look but this is uh you can see how the leaves and stuff have been on for a long time

this is actually considered uh the most beautiful rock i know it doesn look that way right here in new england it got all these giant white feldspar crystals Some of them are huge as big as my thumb They just massive And what this was this was some

seafloor sediment, miles thick, that got subducted underneath a continental edge. And then it started

to melt. And then it started to kind of come up to the surface like a hot air balloon, you know

floats up into the sky here's a nice piece of the meredith porphyretic granite i'm going to walk over

to you so you can really see the crystals look at those crystals oh here's a really good piece

where it's been cracked yeah but that's the uh look at those beautiful crystals there look at

that big piece of feldspar pretty amazing but anyway this piece of seafloor it um there's another

big piece of the ledge that's solid bedrock that goes all the way you know to china so to speak

Anyway, this miles of seafloor sediment that got sucked underneath the edge of a continent

it got pulled down, started to melt, and then it became less dense than like a hot air balloon

It started to kind of come up to the surface. And sometimes it makes it, sometimes it doesn't

And eventually, through plate tectonics, it gets brought to the surface like it is here

So this is a giant, huge piece of granite. And it's many, many square miles

Big area here where I live. My house is built on this. I live just about a half mile away

All right. So now you know what ledge is. It's not that thing that's up on your closet

You know, that's a shelf. This is ledge. All right. I'm Tim Carter. Remember, if you need help geology-wise, building-wise, I do phone consulting

I'm Ask the Builder. Bye