Delaware's history for the last 100 million years or so has consisted of being gently bathed by the sea as it rose and fell over the eons, thin layers of sand and silt being draped over it like sheets on a sleeping child. The sediments have never had a reason (like deep burial or subterranean heat) to become rocks. But from such subtle records geologists can reconstruct how the slight rises and falls of land and sea reflect events on faraway crustal plates and deep in the mantle below. More active regions erase this kind of data.
Still, it must be admitted that the map is not full of detail. There's room on it to depict several of the state's important aquifers, or groundwater zones. Hard-rock geologists may turn up their noses and go swing their hammers in the far northern rises, but ordinary people and cities base their existence on their water supply, and Delaware's Geological Survey rightly focuses a great deal of attention on aquifers.
Beside this map, I have posted two other versions that include the full explanation. The mid-sized version of this map is 800x1200 pixels and weighs 400 KB. The full-sized version is twice that size and weighs 1 MB.
More Delaware resources on About.com:
Delaware Maps
Delaware Geography, State Symbols & Facts
Delaware Parks
Delaware Campgrounds
Delaware Archaeology
About Philadelphia
About Baltimore
About Washington DC
