I don't believe it's an axe. It's sandstone, a poor choice of tool stone for an axe. They usually used hardstone. Basalt in southern New England. And it's not the form our axes take.
The question is, is it an artifact at all? Well, many of our region's agricultural tools are made of poor tool stone, like schist and sandstone, for instance. But, even then, you will notice man made work applied to the stone. For example, these sandstone spades from New England. One can see that they have been shaped to a degree, especially chipped along the leading edge or business end. But, looking at your stone, I don't see any indication that it was actually modified or chipped along the edge.
It has the overall shape of some of our cruder agricultural tools, and it gave me pause for that reason. Looks like it has a handle end, and a bit end. Maybe can't rule it out, being pounded worn, and water worn. But I think the path of least resistance is to conclude it's natural, and not an artifact.