In the rule “The Mosaic” replace

Its Content, which can be a string of up to two characters, and by default is empty

with

* Its Material, which can be any of the Materials listed in the rule Materials and by default is stone
* Optionally, its Inlay, which can be any ascii character. By default a tile has no inlay
* Its Content, which consists of the character of its Material followed by the character of its Inlay (if it has one)

In the rule “Materials” replace

s: Sand. ‘‘colored sand imported from merchant ships or collected on the beach.’‘

with

s: Stone. “simple stones collected from the local river beds”
f: Fine Sand. “colored sand imported from merchant ships or collected on the beach.”