^This is an original remain fossil because the spider-like creature was trapped in the sap and then the sap became fossilized (amber), thus preserving the insides of the spider-like creature.
This is a replaced remains fossil because rock forming minerals attach to the hard part of the skeleton hardening them and then letting the soft parts decay. As you can tell here, the rock forming minerals attached to the outer layer of the fish.

3 is the youngest because it's the last layer deposited and according to the principle of superposition it is the youngest.

1 is the second youngest because it is the layer closest to the top with the intrusion,

6 is the third youngest because according to the principle of superposition, it is under the second youngest layer.

2 is the fourth youngest layer because it is an intrusion to the layers below 3,1,6.

5 is the fifth youngest layer because it is under the intrusion (2) and higher than layer 4.

4 is the oldest layer because it is under the intrusion (2) and lower than layer 5.