Actually, there are some pretty good walnut trees in England and some very fine lumber has been cut there over the years. George Nakashima used some from there and in a issue of Fine Woodworking there was an article on a very fine cabinet made from the figured wood of an English tree cut from the property of a British naval officer,interesting story.Some trees I have cut in Blackhawk county,Iowa showed quite a reddish cast with black streaking. These trees all had one thing in common,they were trees grown where cattle had access and grew with lots of manure around them and I mean lots of manure.The lots around the trees were fenced in and the cattle were concentrated so urine might have been a factor also.
