Dirt and Soil, What's the Difference?

Hello Fort Friends! My name is Moline, and I’m one of the students working and studying here at the Fort St. Joseph Archaeological Project.

Today I thought we could talk about soil!  There are different kinds of soil, and they all can give very important clues to archaeologists when performing excavations.  The first kind of soil that we’re going to talk about is alluvium.  In simple terms, alluvium is basically soil that has been deposited by a river.  Alluvium is typically very fertile, therefore it’s good for growing things.  Archaeologists make distinctions between “cultural” soil and “sterile” soil.  Cultural soil is soil that contains artifacts, ecofacts, and features (the trifecta of archaeological material), which is indicative of human activity (hence, it can be called “cultural”).  Sterile soil is just the opposite.  Sterile soil (also called the B horizon) does not contain any artifacts, ecofacts, or features, and therefore tends to not yield much in terms of archaeological excavations (hence “sterile,” since it is free of cultural remains).

Now let’s talk about zones.  There’s the plow zone and the occupation zone. The plow zone is basically the area of soil that has been disturbed by agricultural activities like farming and plowing.  The occupation zone is the area of soil that leaves cultural remains in situ from the time of habitation. 

Now that we have some basic working definitions, we can start talking about how all of those concepts relate to our work at Fort St. Joseph.  We are doing some exciting things at the site, and that includes excavating in a dump located on the premises!  Because the soil has been so disturbed, and because so much modern refuse is in the areas where we are placing our units, we are facing some unique challenges.  Firstly, there is the issue of distinguishing between modern refuse and 18^th century artifacts (which would be from the time we are most interested in as it relates to Fort St. Joseph).  Secondly, we are having some issues distinguishing between different kinds of soil (i.e., Is this soil from the plow zone? Maybe it’s from the occupation zone?).  At my unit, for example, we are seeing a lot of mottling, which basically means that there is a mixture of different soils.  This many times gives the soil a marbled appearance, and as Dr. Nassaney says, looks a lot like the hide of a giraffe.  Because of the trench digging that has occurred, and the farming that occurred on the land before that, it can be difficult to determine if an artifact is actually in situ or not.  Typically, we see alluvium on top, then plow zone, and then occupation zone, then the B-horizon.  Because of the site being located in a garbage dump that used to be farmland, however, there have been too many disturbances to the soil layers to have a really accurate interpretation of what exactly is going on.

What does all of this mean for our units? It basically means that we are going to have to work a bit harder in interpreting our data, but that’s part of the fun of archaeology, isn’t it?

Hopefully that gives everyone a bit of a clearer understanding of the different kinds of soil and the ways that archaeologists use that soil to study the past!  Thanks again for following the Fort’s activities and for reading!

Best,
Moline