inner layers
- coreCentral essential portion
- depthsLowest or innermost regions
- strataParallel geological layers
- substrateUnderlying supporting material
- liningInterior fabric layer
membrane · dermis · subcutaneous · pith · marrow · heartwood · underbelly · foundation · subterranean · beneath · hidden · insulation · padding · filling · stuffing · onion · sediment · bedrock
spatial position/depth
inner layersouter layers
surface layers · exterior · surface · periphery · crust