It's like this at many old houses. Previous owners of our house have used this spot to bury trash. It's not concentrated in a single area, like a privy, but spread out over most of one side of my shade bed. (One day, it took me over an hour to plant one hosta because I had hit a particularly rich spot and I was unearthing nails and broken china.)
This time, most of the 'treasure' was glass, but there were a few odd items mixed in. In the above photo, which reminds me of a page from one of those "I Spy" books, you will find:
An old purse frame
The handle from an iron skillet
Two different patterns of transferware
Most of the pieces of a broken bottle
and an aluminum Jello mold.
I keep all this stuff, and I store it in two Costo-sized plastic biscotti jars. It was trash to someone, but it's treasure to me.