Answer: Based on your description it is a bit difficult to picture the bark, but what you see may be normal. This tree develops, with age, a very interesting irregular bark patterning with for lack of a better description interesting "scaly plates" which tend to look "shaggy" in contrast to the peeling birch bark we usually picture in our minds when we think of birch. However it could also be the result of some sort of old trunk or bark damage or splitting which has healed in a peculiar way. If you suspect that it is something like this you might wish to consult with either your UMass extension office or a professional arborist to see if there is cause for concern in the long run.
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