They are mostly Devonian rocks deposited in the distal oceans in front of the Acadian Orogenic Belt...

https://opengeology.org/historicalgeology/case-studies/acadian-orogeny/

Here is a good image and some relevant information if you are interested...

https://www.museumoftheearth.org/ny-rocks/devonian-geology

a long, long period of time

about 380 Million Years :)