Thanks Mike, I've just passed that on to my fly tying buddy, he got all excited at the thought of tying up some flies which haven't felt the warmth of the sun in a while...good find!
The book will probably be hard to find. Try searching on evil-bay for a used one (also referred to as the Bay of Evil by some Canadians - something of a link to the Hudson Bay Company).
But also try some of the book search web sites like abebooks.com, alibris.com, and occasionally even Amazon.com And Bookfinder.com is supposed to search all the major book outlets - including the used/rare/out-of-print book sites.
The flys shown in the book are still pretty common today. They are Dame Juliana's List of Twelve Perfect Flies.
Dame Juliana Berners reportedly wrote a book in 1496 called A Treatyse of Fysshynge with an Angle. It was reprinted in 1979 as A Treatise on Fishing with a Hook - but translated into modern English. And Izaak Walton agreed with her 12 flies in his book The Compleat Angler originally published in 1880, but republished several times since.
Good luck on the search for the book.
Mikey - yee ol' grumpy blacksmith out in the Hinterlands