Geology is QE
Geomorphology is GB 400-649
Engineering Geology is TA 703-712
Other areas of Q, G, and T may also contain geology resources
GeoRef is the most comprehensive database of geoscience literature and the best place to start for most geological topics.
Compendex from Engineering Village is the most comprehensive engineering database, covering all disciplines.
USGS Publications Warehouse indexes all USGS publications, many of which are downloadable.
USGS Library is the largest earth science library in the world.
Dissertations and Theses will provide you to the full text of high quality student work that is not indexed elsewhere.
(Great for topic ideas.)