Lines Left upon a Seat in a Yew-Tree

What is unique about this poem is William Wordsworth's use of the long dash. It really made me think and what I came up with is that the lines that were left upon a seat in a yew-tree are the first seven lines in the poem. Wordsworth uses the long dash as a separation which divides the "lines...yew-tree" and his own poetry. I think that he might have come across those few lines and then in a way responded to them through the rest of the poem. What convinces me even more is that in the first seven lines, he is directly addressing a person (the traveler) telling him to stay and wait and then talking about the yew-tree. In the lines following the dash, the use of the word "he" is very common. Wordsworth may be trying to analyze and figure out "who he was that piled these stones..." and he talks about this with the "stranger" or "traveler." The Lake of Esthwaite also put a thought into my head. I looked for images of what this lake is like and it turns out it's a very beautiful part of nature. So maybe someone started writing some lines in this yew-tree, but never got around to finishing it because of the beauty nature. Perhaps nature was calling them, and so they went to explore the terrain rather than finishing up what they started writing - hence the long dash in the poem. It would be nice to know what Wordsworth really meant, but it sure makes you think and every time I look at it from a different angle, I come up with a different interpretation.