John,
The Google Earth Latitude and Longitude for Sam stone near Thoreau's cabin site.
42*26'29.91"N & 71*20'32.59"W

Carl

Carl Anderson – IBM Fellow
Building 045,   3N105
11400 Burnet Rd
Austin, TX 78758
Phone 512-838-0483,  TL 678-0483
Cell 512-689-7327
FAX 512-838-7694