The combination is the one we see is physical and the author one that we can’t see is unphysical
The property that makes slate most suitable for roofing shingles is that it can be split into thin, flat layers.
This means that the roofs of houses and other buildings can be created from slate in order to cover the tops in the best way possible. Other materials are also often used for this purpose, but slate is one of the most popular ones nowadays because of that property it has.
