There were some distinctive shapes in the rock. Coprolites, or fossilised pooh. Both the fossilised stuff itself an some counterparts where a some had fallen out of the shale.
There's quite a lot of this stuff in this one block of shale. Close-up coprolite:
Jurassic marine creatures had to excrete; maybe they were creatures of habit returning to a favourite spot (no reason why 190 million year old creatures shouldn't be territorial or develop habits like creatures living today; prehistoric doesn't mean stupid). Or maybe we're just dealing with an ammonite with an upset stomach. There were ammonites around this Jurassic jakes, here's the remains of one found in the same block 60 cm away from the prehistoric poop: