original_query: What caused the formation of the layer of Pottsville Conglomerate on top of the shale?
query: What caused the formation of the layer of Pottsville Conglomerate on top of the shale on Spruce Mountain?
answer: As the Blue Ridge Mountains eroded, rivers carried sediment down to low-lying areas, forming a layer of Pottsville Conglomerate on top of the shale.