Nice dig! I've seen flask of this type but never one with an iron pontil. There has been some discussion as to whether or not they are American or English - I've always leaned towards American because of glass texture and seeing this one with an iron pontil makes me think it even more likely to have been blown on these shores. I'll be interested to hear the thoughts of others.
Also, FWIW all of the flasks of this type I have seen have had very little wear (even though they were undeniably "old") leading me to believe that most, if not all, were originally wicker covered.