Quoted from hailrazer:
Coins and gems that could easily have been from people in the 1700's that dropped them. Families passed things down a long time you know, and coins were used for hundreds of years.
This. While renovating my kitchen, I found a couple of coins that had been dropped and were under the quarter-round molding. One of those coins was older than the house by a few years... that doesn't push back the date that my house was built.
When my daughter was little, she had an interest in money from other countries. At the time I had a graduate student working for me who was from China, and she brought me a couple of coins from China. As I was helping my daughter identify the coins and when they were made, I realized that one of them was over 300 years old. I tried to return it to the student, thinking it might be valuable, and she laughed-- she said they were still in common circulation, she had picked it from her pocket change, and it was worth less than 10 cents US.