What is the likely construction/material of the basement floor shown below? It's not very flat, and the surface appears sandy. It's almost as if some kind of skim-coat was applied to the dirt floor. I've seen this type of basement floor frequently in old New England homes. What's it called? What's it made of? Is this technique still used today?
Note: answers such as "this floor appears to be partly made of water" are certainly accurate, but don't really get at what I'm looking for.