I don't live and work on a ledge, but on ledge.  In an early conversation when I first moved to Cape Ann someone said:  "We ran into ledge."I had to scramble to use the context of the conversation to interpret what they were referring to--a granite batholith that forms the bedrock of Cape Ann.  The formerly molten material cooled deep under the earth and is now exposed due to erosion by glaciers, wind, and water.  It is part of a terrane--a piece of the earth that is a fragment that originated elsewhere--but became attached (or accreted) through tectonic forces.  John McPhee, one of the best nonfiction writers of our time, has a book titled "Suspect Terrains" where he talks about the accretion of terranes that led to the geologic mixture of the American west.  In my mind, terranes are clearly more suspect than terrains.  The suspect terrane, composed of the granite ledge on which I live, broke off from Africa and attached itself to North America when the two continents collided, prior to the formation of the North Atlantic Ocean.The granite ledge around me creates both challenges and opportunities. Building can be a challenge when you are at a place where the ledge is right at the surface.  I hear stories of pieces of ledge in basements--where it was easier to build around it.  From my observation, it appears that towns that originated as fishing villages are build right on the ledge--Manchester, Gloucester, and Rockport.  Towns like Ipswich and Newburyport  are located in areas where rivers empty into the ocean, leading to deposition and better soil.This past Saturday my daughter and I went to Halibut Point State Park, one of the best places to get a good view of the geology of the area.  At Halibut Point you can also see the opportunity that came from ledge--the quarrying of the granite, most of which ended by the 1930s.  One of the characteristics of granite is that as it is exposed, and the pressure of the weight of material that was on top is reduced, it breaks off in layers, much like an onion.  This process is called exfoliation, and it makes is easier to quarry.I live on ledge, which is part of a suspect terrane that originated in Africa.  I have always wanted to visit or live in Africa.  Does this count?