A question for my friends list, especially those who are into the 19th century

[snowywolfowl]

Tonight during my American Lit class we were discussing Emily Dickinson's poetry, and this poem caused some confusion:

"The thought beneath so slight a film
Is more distinctly seen, ---
As laces just reveal the surge,
Or mists the Apennine."

My question refers to the third line. What is surge and how would it relate to lace? Nobody in my class from the prof on down really knows what this is about on a literal plane.

Thanks!

Dave