 Okay so we have our ripple here and I want to talk about how cross-lamination forms in the ripple itself. So we have our flow speed as always going to the right here and I'm going to draw a bunch of different colors to show what happens. As we marked in the last video we have our attachment point where the flow is close to the bed, our separation point where it's far from the bed, where it leaves the bed and that happens periodically as we go from one ripple crust to the next. So we said that in this area there's erosion of the grains and in this area here we have deposition. So the black represents time zero and we're going to advance a little bit through time with deposition and erosion to see how this actually impacts the grains themselves. So I'm going to erase the annotations because this is going to get a little bit complicated anyway. I'll draw the next one in blue. So what happens is you have erosion in this area so this part tends to go down but you have deposition in this area here. So this part of the line goes up. So basically the grains here have migrated into this area here and the same thing happens on the next ripple here. So I'm going to erase the grains that have moved and then we have the next time step. Our attachment point has moved downstream a little bit and we have erosion from there and we have deposition here erosion and deposition and the lamina up at this top have eroded away and then we'll go for our red unit here. So say our attachment point is now here got erosion and deposition the attachment point is here we have erosion and deposition and then this part here gets eroded away. So what happens is that through time you create these lamina which represent timelines in the rock that are moving downstream and you're eroding part of the ripple on the upstream end. Okay so I've drawn a history of the ripple moving in nice rainbow colors and this is to give an idea of the connection between the bed form and the cross lamination that you actually see. So this lower part down here which is the history of the ripple migration is the cross lamination part. Okay so what we have earlier in the videos we talked about how we have the attachment point erosion upstream of the attachment point and the formation of another layer. Okay so there there are several key parts one is that this part of the ripple gets eroded away and that sand gets transported here and then this layer sits on top of the back of the ripple that's downstream from it. So this set of lamina form at the downstream side of this ripple this set of lamina form of the downstream side of this one and so when you have these sets of cross lamination sitting on top of each other each one represents a bed form that is migrated through that area and left some of the sediment behind. Okay so each set of these lamina that I've drawn and do another one here represents the geometry of the slope of the the downstream side of the ripple and the bottom of that is deposited on top of the erosion surface of the downstream ripple. Okay so basically this this uses the law of superposition again that what's what's underneath is older and so you have this erosion surface forming on the upstream side of the ripple and then the next ripple comes along and the deposits and the sediment gets deposited on top of that erosion surface. So through time it gets buried with successive layers and that erosion surface is what makes these surfaces underneath they get buried that separate out layers of cross lamina. So if we think about if we look at it more specifically each one of these layers that are separating the lamina are the erosion surfaces or microinconformities that form on the upstream side of the of the ripple that migrated through the area first. Right and all of these lamina in here the lamina reflect the geometry of the deposition they have they have some thickness to them and the the geometry that you see in the layers depends on the geometry of the surface. When a grain gets when a layer gets deposited on a surface it roughly parallels the surface sometimes it will pinch out something like that but the geometry of the layer represents the geometry of the surface when the ripple is formed. Thanks for watching!