Historic Architecture in Northwest Philadelphia: 1690 to 1930sHistoric Architecture in Northwest Philadelphia is a colorful and comprehensive look at the rich architectural history of the Wissahickon Valley, and the people who made it possible with a locally sourced building stone, the Wissahickon schist. The simple stone structures of Germantown's origins as a village of German immigrants laid the groundwork for the more elaborate buildings for Philadelphia's rising mercantile class that followed. From the