Eureka's diatom site is an excellent site for information on this topic.
Diatoms are an important element in stratigraphic dating systems.
These pages introduce diatoms, and highlight their uses and scientific applications. There are a large number of GIF images of diatoms which can be viewed at various resolutions. There are also extensive details about their origin, history of research, morphology, taxonomy, their role in geology, biostratigraphy and paleoceanography. Industrial uses of diatoms are reviewed, covering filtration and dynamite. The site provides a series of lectures about the origins of sedimetary rocks.