A spoil heap at Yorkshire Main Colliery has been investigated to determine whether or not the material buried within the heap is being weathered. Samples have been obtained from a borehole through the tip, and control samples from underground. The observed breakdown of the underground samples upon exposure has been related to the material in the spoil heap. It would appear that after the initial, relatively rapid physical breakdown, the material has changed little. Mineralogical and chemical analyses show that the level of chemical weathering does not increase with depth in the spoil heap. There appears to have been little movement of water through the spoil heap. Chemical analyses of the ground-water also shows no evidence for weathering. Small changes have been recorded with depth, but in all cases these are believed to be due to original variations in the material at the time of tipping.