Essai sur le syst?me silurien de l'Am?rique septentrionale. This book, "Essai sur le syst?me silurien de l'Am?rique septentrionale", by Francis Castelnau, is a replication of a book originally published before 1843. It has been restored by human beings, page by page, so that you may enjoy it in a form as close to the original as possible.