With a line level tied to your datum point measure how deep it is at the start of any new level. If you find a bottle of dish measure exactly where it is in the pit. You may want to drawn where it was found on graph paper, and take pictures. After you sift the dirt look closely for any broken pieces of pottery, glass, coal, and bones. There may even be broken arrowheads, or red cracked fire stones from Indians.
Pottery preserves very well.
There are a number of kinds of pottery that were made at certain times in the past. Let's look at some of these. This is pottery made with red clay like flower pots today. The red color is from iron oxide in the clay. When you find a piece of pottery look at the edge to see what color it is.