|Martha's Vineyard Cottages|
In 1817, the American School for the Deaf opened in Connecticut. Children from Martha's Vineyard quickly enrolled at the school, bringing with them their sign language. This, combined with the teachers' use of French Sign Language, and other children's home-crafted sign languages, combined to create what is now American Sign Language.
Martha's Vineyard Sign Language died off as Martha's Vineyard became a tourist-oriented island. However, it remains a fascinating point in the development of language.
You can read the book Everyone Here Spoke Sign Language: Hereditary Deafness on Martha's Vineyard by Nora Ellen Groce here on Google Books, discovered thanks to Boing Boing's article on this topic. I am reading my way through it right now; it is fascinating reading about the adaptability of humans to their environment.