Tim:

My guess is the time periods that these different saw types were in use overlapped each other to quite an extent, making it all the more frustrating to try to date stuff. I mean, the mill I visited that is undergoing restoration, actually operated regularly as a sash mill until 1962!

That's unheard of from what I understand. Not 1862, but 1962! It began cutting in the late 1840s.

This book (I love this book!) gives a good overview of types/dates, but the pictures might be misleading.

For New England, it says:

Sash: pre-1850
Bandsawn: later 19th century
Circular sawn: mid to late 19th century

http://books.google.com/books?id=2W1Lq_n...VQid4wxmCu0kU3Q

Of course, the dates should probably be coinsidered as a general guideline.