Yes, those ponds had sufficient clay present to hold water. I've never had to truck in clay for a pond before, usually before starting a pond you dig a test hole a few feet deep to see what kind of soil you are looking at and also if it fills up and/or holds water. If conditions looked unfavorable (gravel ground etc) then we wouldn't put a pond there. If you have a mix of good and bad material, you might be able to make it work. You always need to make a good keyway where you mix the clay thoroughly and pack it in. If you hit good springs, or have some sort of natural water supply, you might be able to get away with lower quality/less clay. What I mean is that if the inflow of water is greater than what you are losing due to leakage, you'll have a pond.
This was around Wayland, technically in the township of South Dansville, a few miles from Route 21