Ancient Stream Beds in Schodack NY Area

On some of my past digs in the southern Rensselaer County area I have come across a couple of places with what appears to be of the smooth stream bed variety stones. Such is the case recently on Graw Road area. Even though this area has been farmed and developed over the last two and one half centuries and many of the rocks removed for stone walls or disposal. I have unearthed several oval smooth smaller rocks that appear to be the kind one finds along steam beds or rivers. Even from heights there is not a decernable indentation of stream bed activity that I can detect. There was at the end of the last glacier period appx 13,000 to 14,000 yrs ago many streams created and faltered. The slope of the Hudson River Valley would tend to pull streams in an east to west flow from the eastern side of the valley. Perhaps a stream or 2 may have been formed from springs reaching the surface that have ceased to flow. Don't know. I hope in the future to explore this area with time and permission to a fuller extent.