Rob wrote:

The New Hampshire/Vermont slates are said to be very long lasting slates.

Vermont Structural Slate is one quarry. Gorgeous slate.
http://www.vermontstructuralslate.co...e_profiles.htm

I worked on one project (that unfortunately never got built) where the
roof was a combination of the three different slate colors in the top
row of the linked page above. The roof was designed so that the lower
rows of slate were thicker and bigger and tapered off in thickness and
size as the rows progressed up the roof. An exceptionally beautiful
roof with almost a forced perspective look.

It kills me when I see a prime Vermont slate roof and some idjit
patched it with some Pennsylvania ribbon slate.

R