Question: recently i found the remains of a fossil on a piece of slate i was wondering if you knew why it got their (it was down watchet)?

Ceri-Wyn Thomas answered on 24 Jun 2010:

Hi. Fossils from when an organism dies. Generally, organisms with hard parts like shells or bones are much more likely to become fossilised.. Softer tissues like organs and muscles usually decay before fossilisation can occur. In order to become a fossil a dead organism usually gets covered in sediment (most fossils form on the sea floor and I’m guessing your slate fossil did too). As it’s being covered in sediment a lot of minerals present in that sediment start to replace the minerals in the degrading fossil skeleton. These minerals are often the most abundant in the rock- (so a fossil formed in limestone will probably be replaced with calcium carbonate). Once the bone or shell is fully replaced, or in some cases encrusted with minerals, it is well on it’s way to becoming a fossil. Often these sediments get covered by even more layers of sediment and everything becomes very compacted usually flattening the once 3D organism into a flat, 2D fossil!

In the case of your slate fossil: Slates are formed from heating up very fine mudstones. So the fossil would have originally been covered in mud and the minerals in that mud (mainly aluminium and silicon!) would have replaced the hard parts of your fossil creature eventually. If you can describe the shape of the fossil I can probably tell you what sort of creature it was!