- [Voiceover] Another approach is Grain Sequestration Approach; and this one is built on a simple principal is, is that anytime that you are depositing one of these gravels from your source area into your sink, that is one gravel that will now no longer be deposited further down dip. So, in senses, you go down dip you preferentially deposit the coarser grains first because they're the hardest to carry it means as you go down dip, these coarser grains further up dip start to become these finer grains further down dip. And there's a systematic loss of grain size as you go down dip. So, making some assumptions about what kinds of grain sizes you started with by basically what is missing as you go down dip, you can make an estimate of how much is being deposited and for any given area make some sort of an estimate about how much sediment must've been brought in from further up dip to give you the sediments that you have. Of course as you might guess, this is wrought with assumption-airs. So, there's many assumptions have to be made to make this technique work and once again, it works better in the ancient record because you can often get longitudinal estimate, a your sediment as its been deposited just by simply measuring sections in the depositional dip. However, it requires so many assumptions about what was going on in the source area and how this system was moving and depositing that, it also has a tendency to introduce quite a few errors. Once again, in order of magnitude, accurancy you feel pretty good about this estimate.