The \observational content" of geometric logic is discussed and it is proposed that geometric logic is an appropriate basis for a Z-like speci cation language in which schemas are used as geometric theory presentations. A descriptional mechanism of \schema entailment", generalizing type constructions and logical entailment, is de ned and investigated in some examples, and is also used in de ning schema morphisms which are discussed brie y in connection with schema connectives, and with specifying and implementing operations.