RUBBING ROCKS AND THEIR ASSOCIATED LICHENS ON THE PRAIRIES OF SOUTHERN ALBERTA, CANADA. THESE ISOLATED BOULDERS AND COBBLES LIE THINLY SCATTERED OVER THE TERRAIN. AS I UNDERSTAND IT THESE ARE MORE PROPERLY TERMED GLACIAL ERRATICS AS THEY WERE LEFT BEHIND AS GLACIERS RECEDED. THEY SERVED AS RUBBING/SCRATCHING STONES FOR BISON AND PROBABLY OTHER LARGE MAMMALS AS WELL. MANY TODAY STILL PRESENT A POLISHED FACE AS THE RESULT OF THOUSANDS OF RUBS OVER THE CENTURIES. OFTEN THEY SIT IN A SMALL DEPRESSION CREATED WHEN THE SOIL AROUND THEM WAS COMPACTED AND RENDERED INTO DUST BY HOOVES AND SUBSEQUENTLY BLOWN AWAY. MANY HARBOUR A DIVERSE AND BEAUTIFUL CROP OF LICHENS.