I'm pretty sure it's not lamination. Lamination is a faulty planchet due to improper mix in the alloy resulting in areas of metal seperating or peeling away. I have seen wheats with similar on the reverse (I even have a few thrown in my bag of wheats). I'm not sure what it is but am inclined to believe that it is very old glue. I heard that in the old days it was not uncommon for collectors to glue their coins into their board (predecessor to folder) to prevent them from falling out.