http://imgur.com/zWX6WZW This has been in my yard since the house was built 100 years ago in North Buffalo. What is this, a cornerstone, headstone? It's just sitting in the middle of my yard almost as it isn't mean to be moved. It's about 6 inches by 6 inches.
You'll probably get more help over at /r/whatisthisthing, the appropriate subreddit for these kinds of questions.