Geological map of the environs of Orbisonia at Rockhill Gap, Huntingdon County / Second Geological Survey of Pennsylvania ; J.P. Lesley, State Geologist ; Chas. A. Ashburner, asst. geologist ; Chas. E. Billin, topographer.
From Parts (In 6 layers) Depicts: 1878 Last modified almost 3 years ago. Unrectified.
A low resolution preview is shown below.