US 25398781 A description referring to the figure four rubblized oil shale beds 10 12 14 and 16 are shown arranged in two pairs pair b and pair c beds 10 and 12 are an associated pair of spent shale beds which have been previously pyrolyzed and at least partially combusted beds 14 and 16 are a pair of associated raw oil shale beds which are to be pyrolyzed using the latent heat in beds 10 and 12 as more fully described in the above noted application ser no 220 645 in accordance with the invention each of beds 10 12 14 and 16 is u shaped in plan and arranged so that the individual legs of each bed point at one another for example legs 18 and 20 of bed 10 point directly at legs 22 and 24 of associated bed 12 by this means inlets 26 and 28 of beds 10 and 12 respectively face one another and similarly outlets 30 and 32 of beds 10 and 12 respectively also face one another in addition each of these inlets and outlets as well as all of the inlets and outlets in beds 14 and 16 communicate with single common channel 34 thus connection of all of the inlets and outlets of each of the beds to one another by internal piping 33 and to external piping is facilitated since all of the connections can be made in a.