The Thames valley

Bill and Lucas Novak have been discussing constituent ontology.  I wonder if the following analogy is relevant. The geology of South East England consists of clay overlying chalk overlying greensand. The layers have been raised up into two lines of hills and the clay thus exposed has been eroded away.


It makes sense to say that the chalkiness of the Chiltern Hills and the chalkiness of the North Downs are distinct property-instances. But it also makes sense to say that there is one underlying chalkiness appearing in two substances. It would seem that the world admits a duality of self-consistent descriptions and we can choose to use either. But we shouldn't mix them up.