 A very useful concept in sedimentology and stratigraphy is the concept of feces. Feces are groupings of rocks by characteristics that are useful and interesting for the sedimentary questions that you're trying to answer and address, right? So these you would group into, so it's basically, it's a categorization and you choose, the sedimentology or stratigraphy chooses the categories that are useful for their scientific questions. So this is used in igneous rocks and metamorphic rocks as well. For sedimentary rocks, you can base the categories on the things that differentiate the sediments or the rock types that you're interested in. So for example, the types of criteria you could use would be maybe the grain size, any sedimentary structures, sometimes the composition of the sediment, and sometimes you might use all three of these. And one of the reasons that this is useful is that there are certain types of depositional environments that tend to accumulate certain grain sizes with certain sedimentary structures. And so, for example, within a river channel, you tend to get a certain distribution of sedimentary structures, for example, and those sedimentary structures are distinct from what gets accumulated on a floodplain. And that's reflecting the characteristics of flow and the characteristics of the sediment transport. And so we can define, say, a river channel facies and a floodplain facies and describe the typical characteristics of those. And then we could recognize them in other circumstances or in other environments. Okay, so I was just talking about how facies can be related to depositional environments. They're not actually the same thing. So the facies are the characteristics of the sediment or the sedimentary rocks. So these really, really focus on the deposits that are present. It can include unconformities and evidence of erosion as well, but it's really what is present in an environment in terms of the sediment or the sedimentary rock. In contrast, the depositional environment includes a lot of processes plus the sediment, right? So facies can be relative to sedimentary rocks. An environment can be interpreted from the sedimentary rocks, but an actual environment is something that's at the surface. And so processes would be things like fluid flow. Is it water or air? It includes the sediment. And so you can have the grains that are present, plants and animals. So you can have biological processes. And there's a lot more that goes on within an environment that then actually gets preserved in the rock record. Because this is a whole set of processes, you can have an erosional environment and the only thing left behind would be an unconformity in the rock record. And so you can't really have a facies that consists just of an unconformity because it actually has to have some volume of that rock. Thanks for watching.