I think the formation is Indiana Springs and the matrix is soft so the jet of sand/dolomite slowly began removing material from the fossil. Below are before and after images of each side. I took these in a workshop at night in fluorescent light so the detail is not great.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhQWAAoHA7gUfKOf4DRKzjwl2UFTHVAATFu6fkT0IY1QwGGIVP3UfxCOmYco5U3jZgXJXpyl-SVi73NrsBXN0Tdiwe56-Hck8Hn8iHZ3LWg3zJEP3QavjdANd5bhqW_qmkYgMqrkZMSV-dm/s400/BLASTOID-SIDE-ONE.jpg)
This is a very cool tool that requires patience and attention to detail.