 So the sequence of sedimentary structures also varies with grain size and that's because the grains respond differently in the different flows. Each one of these symbols right here represents an experiment in a flume with a specific flow speed and a specific flow depth. So almost always the flow depth is less than one meter for practical reasons. But we know that the flow depth and the flow speed both matter for sediment transport. So each one of these open circles represents a tie, a condition of grain size and flow speed that produces ripple cross laminations. Each closed one here produced dunes and the triangles up here produced upper planar bedding and the crosses produced anti dunes. And you'll notice that sometimes there are experiments that don't quite follow the lines that are drawn. The lines are drawn sort of generally between the fields. And then down here there's a set of conditions with no movement or motion of the grains. And then there's this zone in here and coarse material which is called lower planar. So we can take a look at this diagram there's several interesting things about it. The first is that at fine grain sizes you only have a sequence of ripples, an upper planar bed and then anti dunes. So at a sort of a very fine sand grain size here your sequence of structures is different than it is at something that say a granule or very coarse sand where you have a lower planar bed going up into anti dunes. So the first key point is that grain sizes matter for which structures that you get move. You actually get planar lamination instead of ripples in this zone here because how the grains stick up into the flow strongly affects which ones move. So if we look at an example of large grains, so let's say that these are the average 2 millimeter grains here. One of the things that happens is that they stick up high enough into the flow that grains that are above the average flow move much more easily. So this grain right here has more exposure to the shear and it is likely to roll down to the next spot. And then it's still sticking up some more so maybe it rolls down again and gets caught into the flow. And so the grains actually can't pile up at these higher grain sizes to make the ripples. However, they can start piling up to make dunes. And so we get maybe a grain transporting transported there and if I add some more downstream once you get a large enough high and an anomaly the flow starts getting directed up and then you can catch more grains in the zone here and any grains that fall off the other side will be deposited on the downstream side of a dune like that happens in a ripple. So the second point is that the transitions between bed forms depend on the characteristics of the grains and the structure and the flow and specifically the turbulence.