You will find a complete review with scientific explanations here.
I originally heard about the Haymond Formation in a Training Union class at a Southern Baptist church. A Southern Baptist deacon who was also a chemist gave the class, and he mentioned the Haymond Formation as undeniable proof that the earth is well over 10,000 years old. If you want plain, show-it-to-your-face kind of evidence; this is it.
The Haymond Formation is 15,000 layers of alternating shale and sand. In the formation are numerous burrows which were dug into the shale, then later filled with sand when the next layer was laid. Let's talk for a minute about why this is an issue.
All believers in a young earth believe that the flood laid the geologic column. If the geologic column was not formed catastrophically in the flood, then it must have accumulated over millions of years as it appears to have. The Haymond formation, however, is in the middle of the geologic column. It is not at the top. It is a huge formation extending hundreds of miles across Texas to the mouth of the Mississippi, going deeper as it goes. It is not a fluke; if the flood deposited the geologic column, then it had to deposit the Haymond Formation as well.
This is a fatal problem for the theory that the flood laid the geologic column, because burrows were dug by animals in the layers of the formation. There were 15,000 of them, with enough time between them for animals to dig burrows, live in them, and then have their burrows filled in when the sand came back. How quickly did this happen? I haven't read anywhere that says, but there is no way it happened during the flood because there's not enough time and animals don't repeatedly dig burrows far underwater in a turbulent world-wide flood.
Basically, this formation represents at least 15,000 years of geologic time, and there are many strata of deposits both above and below it. The world simply cannot be 10,000 years old, and the flood cannot have laid the geologic column.