I have to write a brief geological history of a region starting with the oldest events with schist being the oldest it says i should not speculate but concentrate on the evidence

Question

have what i wrote on the right lines if not can you give me some pointers

The schist would have probably originally been deposited first as a layer of mudstone, which through metamorphism formed into the layer of schist. An unknown layer of rock above the schist would have been present for the gabbro to then intrude into it (it could have formed by rapid cooling on the surface). Then through erosion/ weathering, the layers of rock above the schist would have eventually exposed the upper part of gabbro intrusion, finally more than one layer of sandstone would have been deposited and lithified (by being compacted and cemented) to form sandstone. I would assume the sandstone wasn’t present when the intrutsion took place because it hasn’t gone through the phase of metamorphism