Welsh emigration
As you are probably aware, immigrants tended to clump in certain areas on arrival in the US. The little community of Delta, Pennsylvania, which is right on the Pennsylvania-Maryland border not far from Baltimore, is almost entirely inhabited by descendants of Welsh immigrants who came to work in the slate quarries. Delta supplied a good part of the slate used in the mid-Atlantic states for roofs and other building purposes for many years, until slate was largely replaced by asphalt shingles. The Deltans (Deltites?) still seem to try to keep up ties to the mother country; a couple years ago I saw an announcement of a concert by a Welsh men's choir who had been brought to Baltimore by a club in Delta.