Its called an Oak Gall -

http://www.gtcd.org/cgi-bin/content/content.cgi?db=content&uid=default&ww=on&a mp;id=314&view_records=1

Apparently there are lots of different types - but likely they are harmless to the host tree. Interesting biology and interation between insects and trees - never ceases to amaze me.

Plots still got lots of ferns - love that "North Country Feel" - wish we had some oaks down south where I am!

FH.