Cruising down the ridge in central Pa. late afternoon in the fall and looking into the lowering sun. It wasn't blinding yet but still a factor. Suddenly, there was a another glider coming at me head-on and quite near my altitude. I instinctively buried the stick. There was no thinking involved. He passed over me with maybe 50'(or less) separating us vertically. There was no lateral separation. Had we been at the same altitude our wings would have hit, maybe even striking each other fuselages. I don't know who it was and no one reported anything like this once all were back on the ground. Either he never saw me or maybe was flying from another field. It scared the crap out of me. That we didn't collide was simply a matter of luck.