Abstract: Apparatus for unloading a top unloading mine car that is mounted to pivot about a horizontal axis extending along one side of the base of the mine car includes a hoist chain detachably connected to the mine car at the side opposite the pivotal axis. The hoist chain extends upwardly over a pulley mounted on a positioning crank arm. The pulley moves on rotation of the crank arm from a position substantially vertically above the connection means when the mine car is in an upright position to a position above the pivotal axis. The hoist chain continues around a pulley mounted on a drive crank arm and then to an attachment of restricted mobility. The drive crank arm and the positioning crank arm are rotated in a single direction by drive means which are adapted to rotate the drive crank arm at twice the angular velocity of the positioning crank arm.

Abstract: A modified in-situ retort for the retorting of oil shale is constructed by mining an open space having a volume of twenty-five to thirty-five percent of the volume of the retort in the bottom of the retort and thereafter blasting the oil shale that is to remain in the retort as rubble in a manner to cause random free fall of the shale particles onto the rubblized bed. Blasting occurs sequentially from the bottom of the unfragmented shale immediately above the open space to the top of the retort. At each blast, there is an open space below the shale to be broken in the blast having a volume at least one-third the volume of that shale, and the timing of the blasts is such that movement of the broken shale is not interfered with by shale broken in the preceding blast. There is no withdrawal of oil shale that would cause downward movement of the rubble that is to be retorted in-situ. The resultant in-situ retort is characterized by a high and uniform permeability.