Along the 42N latitude, river bridges built in the 1800s and early 1900s with stone supports had a problem; that being the destructive effects of the freeze thaw cycle, ice flows and floods. All of those forces could potentially weaken the stonework and eventually cause bridge failure. To counter the massive pressure on the stonework a simple solution was devised.
Large iron staples were pounded into the finished quarried support blocks. This helped to keep the orientation intact and resistant to outside pressure. Staple examples seen today at this former bridge site were garbled in various positions.
A newer bridge located just a few yards from this site consists of modern materials (steel, iron, concrete.) The former bridge's stonework has been re-purposed as river bank rip-rap.
At this location only three large staples examples were found in the large chiseled stones. Channel your inner King Arthur abilities to pull metal out of rock, otherwise there is no budging these stone staples as souvenirs. But then what would I do with them? Know that.