Rich,
That looks similar to the one I saw in the antique shop except, as I recall (risky at my age), the top of the chalk chamber was more or less flat and the whole thing was more squared off. If I were to build one, I believe I would incorporate a lid for the chalk chamber. European habitation goes back to the 1600s in these parts and I have no reason to believe it was not colonial, but one cannot be certain.