"What is it?" Wednesdays!

Added close up, as big as I could get it:

Alright, we need help. From time to time, and more often than most archaeologists would like to admit, we don't know exactly what we're looking at.

The St. Johns River Management District called us to come take a look at possible cemetery sites and get them recorded on the state's master site file. We got out in rural Putnam County when we found this first candidate for "What is it?" Wednesdays.

So...WHAT IS IT?

We have a guess but want to hear from you!

Here's my field notes for more details:

Feature found in rural Putnam county on SJRWMD land, not associated with any known historic site. "Cross" is different material, softer sandstone and broken off on the ends. In the back there are three bricks propped behind it and the cement is set across the entire back. Slab is roughly 60 x 75 cm and headstone height is also 60 cm. Feature was oriented E-W on the dot, and we found more letters. "M" at the top as you can see, "Colob" in situ, and then we found a "U" and an "N". Short slab could probably just what they were able to "borrow", but land manager also asked if it could be an infant or a pet. No Colobun's listed at Putnam historical society.