Surface bridging problem

Hey guys

I'm looking at this surface bridging definition i found online 

http://formularch.blogspot.com.au/2012/05/gh-surface-bridging.html

Basically its two surface and lofting them by surface to create a column 

I'm trying it out on one surface that looks like a "C", unfortunately it didn't work. I think I have to split the list of surfaces in to two list but I'm not sure how to do it with my limited GH knowledge.

Can someone have a look?

Thanks in advance.