I've been trying to remember this thing for years and just found it online. Yay! I knew it was Sherwood Anderson but could never find it when I'd try looking through Winesburg, Ohio. I'd remembered it as "two oddly similar human atoms," which doesn't change the meaning much, I don't think.

In that high place in the darkness the two oddly sensitive human atoms held each other tightly and waited. In the mind of each was the same thought. "I have come to this lonely place and here is this other," was the substance of the thing felt.