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My sons and I have been searching different formations in MD/VA for many years so we know how to recognize the different formation layers and have a good idea where to find/or at least check for micro sites/micro lenses. My sons have also been collecting the Eocene/Oligocene formations of Nebraska for years so again they know how to recognize the formation layers. My younger son Mel moved to South Dakota in 2018 and began to also collect the Lance Formation and Hell Creek Formation. However he is still learning the different formation layers. His interest is dinosaur fossils from these formations. My interests are the much smaller micro dinosaur fossils as well as the micro mammal, squamate, amphibian, and fish fossils. I’m always bugging him to send me micro matrix. He sent me matrix this Fall. This post is about one batch of matrix. Mel’s first approach was to send matrix from small areas that have high density surface concentrations of teeth and bones. Where Mel is collecting is more flat and rolling with different Hell Creek layers exposed on the surface versus bluffs and small cliff faces. Mel for Thanksgiving sent me a large USPS priority box of matrix (around three gallons) from a small 6 ft. by 6 ft. area that had a high concentration of dino teeth on the surface. Although sand/clay based this matrix was hard as concrete. I had to use a rock hammer and a small hand sledge hammer to break what he sent into more manageable pieces (definitely not recommended if you are looking for larger specimens). That said the matrix broke down completely in a single day in buckets of very hot tap water and dawn dish soap. I would every few hours use finger pressure to help break up clumps. There was very little residue left after breakdown of this matrix. The below picture shows the residue from about 1/3 of the matrix or around a gallon. The below picture shows what I found. On the left maybe some petrified wood? Doesn’t really look like bone. Maybe geologic. In the middle there is a really nice Croc tooth (4mm), seed (5mm) (maybe modern?), and a partial gar fish scale (7mm). On the right there are several definite small bones and a few specimens that could be bones. Looks like a terrestrial/fluvial environment. What I found was nice but not worth the effort to remove the matrix, send it to Virginia, break the matrix down, and then to search it. Although like I said earlier, there was very little residue after breakdown, so it took only about 15 minutes to search all of the residue. Sampling different sites/layers and trial and error can be extremely tedious and non-productive if you really don’t understand the formation layers and how to recognize them in the field. So I reached out to a TFF member for advice and insight. He explained the matrix types and gave advice on where to take matrix samples. Taking matrix from areas with high density surface concentrations of larger fossils is one way to sample for micros like Mel did for this matrix. However TFF member cautioned that lots of times these concentrations of larger fossils got washed from another layer to the current area years ago and that the underlying layer may not contain much at all as seemed to be the case with this area/layer for this matrix. When you find a good micro site/layer it is very rewarding in the micros that you can find but these sites/micro layers can be difficult to find especially if you don’t have a lot of experience with the Formation. If anyone reading this post has any advice or insight for looking for a Hell Creek Formation specific micro site/layer please post it in a reply. Marco Sr.