Abstract
The contrasting nature of thermal aureoles that surround mid-Carboniferous alkaline-dolerite sills and early Permian quartz- dolerite silk of the Midland Valley of Scotland and northern England is described. The development of the aureoles is influenced by the degree of consolidation of the sediments, their volume of pore water when invaded by the magma, the time period between deposition of the invaded sediments and emplacement of the intrusion and the degree of organic maturation at the time of intrusion. A correlation exists between the logarithms of the thicknesses of sills and thermal aureoles of the quartz dolerites. Equivalent data for the alkaline dolerites lie more than two standard errors from the regression line for the quartz-dolerite plots.