Thickness of the Smithwick Shale

http://books.google.com/books?id=Q5vnAAAAMAAJ&pg=PA26&lpg=PA26&dq=Smithwick+Shale+in+Eastland+County+Texas&source=bl&ots=uiUYjFzy0s&sig=eE4zzwM5JlZD_3883jh0spZS8Hg&hl=en&sa=X&ei=yBEGUeXTFZT_qQHY2YCoDg&ved=0CEEQ6AEwAg#v=onepage&q=Smithwick%20Shale%20in%20Eastland%20County%20Texas&f=false