 So there are two more processes I want to talk to you about. One is the inclusion of clasts into rock and what they tell you. And the other is cross-cutting relationships. Now cross-cutting relationships are interesting because there was a scientist in 1700 by the name of Hutton. And he worked in Scotland and he worked down in the mines. And you could see he had country rock like the rock you see around us here with volcanic material that had squirted in through it. We call them dykes. And so he logically worked out that those dykes that cut into the rock were younger than the bedrock that was surrounding him. And so it's another one of those principles, like Steno's principles, where you know that the younger rocks are sitting on top of the older ones. When you have cross-cutting relationships, we know that the rocks that are cross-cutting the other rocks are progressively younger. And you can get a series of events. So you may have more than one dyke swarm cutting across. So you might have an early one and then another one that cuts across that and then another one that cuts across that. And so that is getting progressively younger. Now the next thing I want to talk to you about are included clasts in sedimentary rock and what they can tell you. And so there's this famous story about the geologist that was training the NASA astronauts who were a bunch of flyboys. They did nothing about science. And so he was trying to just teach them a crash course in geology. And he took them out, he was from Caltech. And he took them out into the California desert. And he got into a place kind of like this except at the bottom of a big mountain where a big alluvial fan deposit came out from one of these canyons. And he said the easiest and quickest way to figure out what's up in that mountain is to actually look at all the clasts that are sitting around in this valley floor. Count how many you can find and we'll compare it to the geologic map later. So anything that was up in that mountain you'd find in the clasts of that alluvial fan. So that that fan material ultimately will get lithified in the rock record. And most of you will know that a rock that's made out of big chunks of other rocks is called the conglomerate. And those conglomeratic rocks can tell you about what the surrounding countryside was made of in terms of the different clasts that make up that conglomerate.