The definitive work on the history of Ogam alphabets is the Ogam Tract in the Book of Ballymote, a collection of tracts gathered together and published somewhat elegantly. The Ogam tract illustrates about seventy different alphabets. There are sixteen of the Ogam variety, of which the sixteenth is the variety most commonly seen in Irish stone inscriptions.
Until recent times it was thought that the other forms of Ogam illustrated in the Ogam Tract were merely Monk’s play at creating secret codes. However, in the 1970s archaeologists uncovered samples of the type 1 Ogam in structures of Spain and Portugal. This proved that the Iberians had come from the Iberian Peninsula. It also proved that the numbering of the alphabets in the Ogam Tract indicated a form of dating. The earliest alphabets listed in the tract being the oldest historically.
As Madeleine L’Engle once said through one of her characters, it is easier to travel to some other when here before you go to that other when there. So having placed the particular alphabetic script denoted by Ogam Type 1 as having been in use on the Iberian Peninsula during the era 800 B.C. to 500 B.C. for both Celtic and Phoenician writing, we can make the jump of place during the same era to New England. The same type of Ogam in both Celtic and Phoenician texts are found in New Hampshire and Massachusetts.
Mystery Hill, North Salem, New Hampshire, is an example of a preserved stone structure dating from this early age.
Source: Fell, Barry, America B.C.