 So we can also use stratigraphic columns to represent significant thicknesses of rock. So the photo on the right shows two of the geology 109 students from a few years ago using a Jacob staff to measure the thickness of rocks, which are turbidites. So each one of these beds that's sticking up is a sandstone. And then the darker beds in here that are weathering out a little bit recessively are mudstones. And so in this particular case there are thin turbidites with various of the boomer faces and they're separated by the mudstones, which again you can see under the student's foot here, which is the Baumae sequence. Then when you get over here we have a much thicker sandstone, which also represents turbidites. It's actually a couple of flows. So this is coarse sandstone here. So we have a big change in the character of the beds between where they're measuring and this thick sandstone here. So what they're doing in the field is measuring the thicknesses of those beds, characterizing the grain size and recording it in their notebook using a graph, something like we have on the side here. So we will start our stratigraphic column right under this geologist's foot. And the Jacob staff is a 1.5 meters long and I marked off the approximate 10 centimeter zones here. So we're going to measure and draw a stratigraphic column for about a meter and a half to here and then we'll get to the coarse sand. So let's say 2 meters. So we need 2 meters total. And I happen to know I have 30 lines here, but we're only doing 10. We could do 10 centimeters per line, which would represent each one of these. And my centimeters didn't count my balls. So this would be 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 10, 20, 30, 40, 150, which is 1 Jacob staff length, 10, 20, 30, 40, 50, that's 200. And I think that's about all we'll draw right now. So it's mostly sand. I mean, it's mostly a mix of sand and shale, right? So we'll say that the mudstone, the grain size is between clay and silt. It's a mix between those two, but we're starting out on a sand bed. And we can't tell necessarily what sand size it is. So I am going to assume that it's medium sand. And we have a little less than 10 centimeters thick here. So we have our sandstone here. Then we have a little bit of a shale in this stone right here. And if we look latter, it looks like there are a couple of very thin sand beds. But that goes up to 30 centimeters, 10, 20, 30, before the next big sand bed. So if I was in the field, I would be drawing this precisely, often using a ruler. There are a few sand beds in there, but they're sort of too thin for me to measure. So I'm going to draw a line coming out just to represent those sandstone beds. Well, I may be there too, I'll draw that too. And so I can make notes about the texture here. And I'm going to basically say a thin SS for sandstone beds. And I'm going to say that they're schematic, meaning that I didn't measure those exactly. Then we have a sandstone bed that looks like about five centimeters thick. Maybe a mudstone that's five centimeters thick. So I'll draw that's five centimeters as half that. And then we have some mudstone again. And then we have another sandstone that's maybe not quite 10 centimeters thick. And then we have this area that looks like it's mud. If I look over here, I'm seeing some mud and then some sandstone beds. And then this thick sandstone again. So this is 10, 20, 30, 40, 50, 60, 70, between 70 and 80. I have a sandstone bed that's 10 centimeters thick. So 50, 60, 70, and 80. So I have a sandstone bed here. And between that, we have two little sandstone beds and some mud. So I'm going to do the sandstone beds, the thin ones, schematically again here. And then we have mudstone between the muds. Let's redraw that a little bit finer grade here. So then we have a mix of those again coming up. And I'm not going to draw all of them. So this goes to about a meter and a half in here. And then if I was in the field, I would measure it. But let's say that this is another 50 centimeters. So that means that this coarse sand would start at our two meters up here. So that is a very, very flat bed. And it would go all the way out to coarse sand, which is this one, I think. And then goes up here. And it's mostly massive here. And then if I was measuring in the field again, I would basically fill this in with the beds of sandstone and mudstone. So I am using the term shale as well. When I'm doing my strat clones, I usually try to say mudstone because sand and shale will start with us. So what we do is we basically can measure successive beds. And when we're in the field, we can actually see the sedimentary structures in them. And so we could put in the sedimentary structures. Say this is a planar lamination. There are also ripples in these rocks. So they happen to be turbidites. So almost always they have the planar lamination on the bottom. And then the ripple lamination is above that. But maybe they don't all have that. So if I was in the field, I would actually be recording what I see and only what I see. So let's just focus on this part that I actually filled out here. So this is a stratigraphic section that represents this component of rocks in through here. So with time and practice, you can measure tens or even hundreds of meters of section like this. And it gives you a record of the grain size and the sedimentary structures and the thickness of beds and how they are organized relative to each other. Thanks for watching.