A query on software design/architecture

In book 'Patterns of Enterprise Application Architecture', following is stated:

When thinking of a system in terms of layers, you imagine the principal subsystems in the software arranged in some form of layer cake, where each layer rests on a lower layer. In this scheme the higher layer uses various services defined by the lower layer, but the lower layer is unaware of the higher layer.

On other hand, in book 'Agile Principles, Patterns, and Practices', following is stated on Dependency-Inversion Principle:

High-level modules should not depend on low-level modules. Both should depend on abstractions.

This sort of confuses me. Am I mixing two different things here?