Any geologists out there?

[mbrssmd]

The photos below are from the base of the hillside where my grapevines are planted. In certain places I went through a lot of this stuff when digging the holes for the vines. As I hope you can see, it is a layered mineral, and was actually 'relatively' soft and easy to break up when digging the holes (although my back would probably disagree...).

I would be grateful for any folks with appropriate expertise enlightening me as to what this type of stone is.

 

[franc1969]

I am not a geologist, just live in Maryland. Looks like what I've always called shale. Some fields are full of it, 'easily' dug through. That's relative, of course. I am curious as to exactly the composition of this stuff.

 

[VinesnBines]

Shale. Composed of clay and silt.

 

[mainshipfred]

Judging by the thin layers I see I'd have to agree it's shale.

 

[srcorndog]

Or is it slate does it break in layers feel lucky I have granite under my farm rock quarry is 3 miles away part of stone mountain!

 

[RolandD]

My vote for shale, as well.

 

[bstnh1]

From a science site: "When muddy sediments are buried and compacted for a long time, they form shale. When shale is buried deeper, for a longer time, and heated by the Earth's crust, it forms slate."

 

[Sinoed09]

Looks like shale - dark clay interbedded with sand. Shale needs both pressure and a source of material to form. Since the layers are really thin it didn’t have a large constant supply of fine sediment so it wouldn’t have been at the outflow of a river for example. The dark colour is from organics. This was probably at one time a lake bottom that had a seasonal freshette bringing in sand. Many shales have trace fossils that can pinpoint the time period It was deposited in. You didn‘t say where exactly where you are but in most provinces (and I‘m assuming states) you can look up regional geology maps. The maps will tell you what the formation is and all of the different layers. Each layer is described with time period, depositional environment and key characteristics. The trouble is then just figuring out which “layer” you’re digging in.

 

[mbrssmd]

Sinoe09: Thanks for that info and suggestion. We're in Central Maryland, about 15 miles below the Mason-Dixon line. On my list for this winter is to get a little smarter on the relationship of minerals and our 'terrior' to my own wine-growing, however humble. I've been setting aside various articles I found after the first few responses to my query came in. I very much appreciate your pointing me to regional geology maps. And as an old dinosaur myself the idea of figuring out the time period layer where we are is rather intriguing.

 

[Sinoed09]

I very much appreciate your pointing me to regional geology maps. And as an old dinosaur myself the idea of figuring out the time period layer where we are is rather intriguing.

You’re welcome. I graduated with a Mining Engineering degree so I studied a lot of geology. I’m not sure where the Mason-Dixon Line is but your best resource will be here: Maryland Geology . I’m guessing you’re somewhere in the Atlantic coastal plain? That region covers the quaternary (today) to the triassic (200-250M years ago) . The Triassic period was when the first cells were formed which is also known as the evolution or beginning of life, so there is quite a bit of ground to cover.

If that’s the case you’ll want to look for the first four types of trace fossils on this page - Characteristic Maryland Fossils .

Take a look at the distribution map to narrow it down a bit - Fossil Distribution .

Shale is one of the best types of rock to look for fossils because the layers often trapped mollusks and plants. If you have a couple pieces see if you can bang or knock it to get it to split naturally and then very carefully examine the new surfaces. You’ll want a jewellers loupe or something similar, some fossils can’t be seen with a naked eye. Be very very patient and diligent - you may not see anything at all the first time or two you look but you need to train your eyes. The fossils can appear as a darker “spot“ in the rock or as impressions. Once you find your first one it becomes much easier. When you start finding fossils you’ll know how old the rock is and can get an idea of climate and what was happening at the time.

Good luck!