Answer:
1. I
2. B.
3. F
4. M
5. R
6. H
. . . I don't see a seventh letter or a seventh layer. . .
Explanation:
On the presented image we can see several different layers of rocks that have formed over several different periods of time. It is not layers that have superposition, but instead there are several disturbances that have resulted in displacing some of the layers from their initial position.
The layer I is the oldest, and it is the basis on which the other layer lie.
Layer B is the second oldest and layer F is the third oldest. We can see though that the left side is higher, while the right side is positioned lower. The reason for that is geological activity that has pushed one side upwards, and moved the other side downwards, most probably a fault.
Layer M is the fourth oldest layer, and it is easy to see that this layer lies completely on top of layer F, just that it has been cut through by an intrusion.
Layer R is the top layer, and it is the second youngest. As a layer though it is the youngest, and it is almost uninterrupted and lying on top of all the other layers.
With the letter H we have the youngest geological structure on the image. It represents an intrusion, and it is not a layer. We can tell that it is the youngest because it has managed to cut through all other layers, which is only possible if there were already preexisting layers when the intrusion occurred.
