 So in this video we're going to talk a little bit about stratification, bedding and bedding planes, lamina, cross lamination, cross stratification, cross bedding and bed forms. Like what what are those? So the first thing is stratification. So strata equals layers. Okay so stratified rocks are rocks with layers and so if we look at this picture here you can see that there's a layer here, there's another layer up here, you might divide out that thin one in there and as you come down here you can see that there there are plenty of layers. So we would say the stratification in this rock varies vertically because down here where we have the older beds they're thinner and then up here they're much thicker. So I've been using the term beds and bedding planes so each grouping of rock that breaks into a layer with a top and the bottom is what we call a bed and so in some cases the the beds continue for a long time laterally but then in other cases like this one right here as it comes up and around over this corner it pinches out into something that's that's very thin. But in general beds are single layers that continue at least somewhat laterally. So the beds themselves are separated by what we call bedding planes and so if we look for example down here we can see a bed and then there's a little bit of topography going back to this dashed line in here and if you look down on that surface it'll it'll be somewhat planar and so we have the term bedding planes and those are the boundaries between the beds so beds are separated from each other by the bedding planes and they're not always completely planar but they often are. So then we have structures that are within beds and those are often called the lamina right. So lamina are layers within bed and within beds and you can see some in this picture here where there are individual layers that come span across this rock and this particular rock does not actually break into beds like the one does above and that's in part because it's all about the same grain size and deposited in a similar way. Now we're getting down to the idea of cross lamina, cross lamination, cross stratification and things like that. So if we look at this image it has both cross lamination and cross stratification and I'll talk about the difference between those in a minute okay and this the cross part of these terms comes from the idea that the layers inside the beds are not parallel to the beds themselves. So this image doesn't have very strong bedding but there is a bed boundary in here roughly sort of broken up and if you look at the layer at the bottom there are lamina that are roughly parallel to each other. If you look up in this layer here you can see that they're lamina that are curved. They're not parallel to that to that bed boundary. What they do is at the bottom they sort of pinch together and at the top they're a little bit wider again and there's some variation and they cross each other a little bit in different ways here. So this geometry where some of the layers inside the bed are at this angle to the bedding planes themselves and there'll be another one sort of roughly in here. That's the cross stratification or cross lamination and the difference between these two is usually how big they are. So the lamination is for small cross layers and the cross stratification is for larger ones just in terms of the terminology and then down here because these are planar approximately parallel to the bedding we would call these planar lamina. So I'm going to show you another example here that has some really nice cross lamination and also some contortion in here. So if we look at this zone right in here we can see that there are a lot of thin layers that are changing geometry laterally. So some of them are truncated against other ones. So for example here are some that come up and they're truncated at the surface here and there's some lamina sort of pinch and swell over that and then this area in here is contorted and that's probably from deformation after the sediment was deposited. So here we have some cross lamination and I'm saying the lamination because the layers are very thin and small. So you can tell by the size of the mechanical pencil here that these are really really fine layers and that's in contrast to this image above. Again we have the mechanical pencil up here. These layers are much coarser. The grain size is also coarser and that's why we call this cross stratification.