It appears to me...
I just completed a book titled Flies and Fly Patterns of the Great Smoky Mountains for Stackpole Books that will be published in 2013. It covers about 60,000 words and is a pretty detailed work on a fairly narrow subject. An entire chapter is devoted to the Yallarhammar fly. I included everything I could dig up about the fly. Much of the tidbits of information are contradictory, but I included them any way.
After making a fairly comprehensive study of the pattern, my theory is that the Yallarhammar was tied as a wet fly, more than likely with a peacock herl body as opposed to a willy nilly, palmer hackled sprig. This is not say that the two styles did not evolve at the same time. However, if you look at the flies used in the waters of GSMNP between 1840 and 1900, you cannot help but see that fly patterns with long bodies were most prevalent. I am strongly of the opinion that the earliest fly tyers of the region drew inspiration from the flies they saw used rather than setting out on creative courses. Itís just my opinion.