This is always a controversial one, so I will do my best to avoid any of the obvious areas of disagreement by only using relative terms.  The terms I use and the details have been used to identify rocks (famously by the canal builders of England in the 18th century) and the system was developed by creationists. 

1) There are layers of rock that contain fossils.
2) Particular fossils are always found together in rocks .
3) It is possible to identify a rock formation from the fossils found in it, for example Devonian rocks can be identified around the world by the particular fossils found within those rocks such as Prototaxites which is characteristic of the Middle Devonian period.
4) The layers of rock with different fossils are nearly always found in the same relation to different layers (for example fossils of the Devonian Prototaxites is always found in layers below the Carboniferous Cycadophyta)
5) In the cases where the layers are found the opposite way round, obvious distortion of the rocks are seen.

What this means is that we can say categorically that in the Devonian the first trilobites and ammonites are found in the fossil record, and that after the Permian rocks there are no more trilobites and that after the Cretaceous there are no ammonites found.