Shells in limestone? Found in the Blanco River, TX

[txqueen9]

We stayed at a private ranch this weekend in Kyle, Texas (Hays County). The Blanco River runs right through the property, and tons of rocks line the shoreline. We know absolutely nothing about rocks or fossils, except for what you learn in 5th grade science and that they're pretty cool. But we found some neat rocks that have impressions of shells and some with shells embedded in them. A quick google search points to the rocks being limestone, but not sure. Any help identifying our little treasures is greatly appreciated. Photos of 2 different large rocks are below. Thanks in advance!

[JohnJ]

The Blanco River cuts through many Cretaceous formations upstream of Kyle. It looks like a variety of bivalves in the first rock (photo 1 & 3). I do see some Neithea sp. shells among the others. Your second photo is the internal cast of a rudist. These fossils are common in the rocks upstream of Kyle.

Welcome to the Forum.

[txqueen9]

Thank you! We figured they weren't especially rare, but for us city folk they're pretty interesting. We brought back a bucket full of a variety of rocks, so it'll be fun to learn about them.

Thanks so much for your quick reply.

[JohnJ]

I find many of our common Texas fossils interesting. You may want to pick up or download Finsley's book.

[txqueen9]

Thanks for the suggestion. Just downloaded the Kindle version. I'm sure we'll be up all night now.