This little park is one of the gems of Gloucester. It is said that the name comes from a freed slave named Ralph who settled near the Chasm and built many of the rock walls that remain along Hesperus Ave. Visiting the chasm became a popular tourist attraction after the Civil War.
All along this coastline, there are reminders of a luxurious past. Expansive mansions are present all along the shorelines leading to the nickname “The Golden Coast”. Look a little closer, and you’ll see a story written in rocks of a time much older than just this past century.
Our coastlines in Massachusetts, particularly Cape Ann, boasts bedrock of a foreign origin. The Cape Ann Granite, which is part of the Avalonia terrane, is the dominating lithology. As an offshore island arc, Avalonia collided in between the terranes of Laurussia and Gondwanaland during the formation of the supercontinent, Pangea, circa 350 Million years ago. Pangea reigned as a singular land mass for most of the Paleozoic, until Mesozoic rifting began breaking it apart. A large chunk of Avalonia was ripped off by the diverging boundary and traveled east across the young Atlantic where it became the core of Europe and the British Isles.
During the evolution of this event of rifting (spanning many millions of years), a swarm of hot mafic dikes developed throughout the granite following new planes of weaknesses forming within the rifted rocks. A spectacular outcrop that contains a portion of this dike swarm is here, at Rafes Chasm in Magnolia. A short walk in the woods will bring you out onto bare rock all the way to the sea. The Cape Ann granite is what appears first; bright salmon against the blue of ocean and sky. This granite is felsic in composition. Its dominating mineral is albite, followed by quartz and k-feldspar, and with the rare appearance of mafic minerals; if they have not already been weathered out preferentially. Dotting the outcrop are “dark fingers of the magma” that have pushed their way through the granite, mafic dikes. The main outcrop at Rafes Chasm has three dikes. The coordinates will bring you to the most impressive one.
To claim this cache, send me the answers to the following questions (do not post the answers with your log):
1. In your own words, how do you think this Chasm formed?
2. How deep and how wide is the Chasm?
3. What is the orientation of the Chasm? (Using a compass or using another method)
4. Post a photo of yourself at or near the posted coordinates. (optional, but encouraged)