I’ve known about this for years, never documented it.  I’m calling it a rock swirl.
  It is right on Cameron’s Line.  I studied that formation when I did my
  Independent Study on Soapstone Quarries in 1976.
  (Don’t do the math!  I’ve heard it is still referred to by some.)

It is an overturned thrust fault.

Here is what it is made up of:

  from the Connecticut Geological Map
CH - Cambrian, Hoosic Schist, which is a gray, rusty weathering,
 fine to medium-grained schist.  And poorly layered schistose-gneiss,
 composed of quartz, biotite and plagioclase.

Ygn - Proterozoic, Layered gneiss, gray, medium-grained, well layered gneiss

Ohc - Ordovician, Harley Formation, carbonaceous schist facies, gray,
 rusty weathering, fine to medium-grained schist and granofels

Or - Ordovician, Ratlum Mountain Schist, gray to medium-grained schist and granofels.

CL.- Cameron’s Line
This is a thrust fault, formed during the North American and African collision.
 
To get more information, you might want to do a search on the Taconic Orogeny.

Here is a close up of the geological map of that area.