The pelitic envelope of a basic and ultrabasic intrusion, together with the pelitic xenoliths, have been studied by field and microscopic examination, and 14 chemical analyses of the hornfelsed pelites are given. Eighteen chemical analyses of unhornfelsed pelites from the region are available for comparison. There was every gradation from biotite-acid andesine-quartz-fibrolite-garnet "regional" schist through cordierite-prismatic sillimanite-labradorite-magnetite-biotite hornfels to spinel-magnetite-cordierite $\pm$ corundum $\pm$ orthopyroxene hornfels as desilication and dealkalization occurred. The $SiO_2$ content, 46.2 per cent, and $Na_2O + K_2O$ content, 6.2 per cent, in the average unhornfelsed nearby pelite fell in the xenoliths to less than 10 per cent $SiO_2$ and less than 0.25 per cent alkali, while the $FeO + Fe_2O_3$, 12.0 per cent, and MgO, 3.4 per cent, rose to over 40 per cent and 9 per cent, respectively. It is suggested that the composition of the material removed from the xenoliths to the ultrabasic magma had a composition resembling, but not identical with, that of Daly's average subalkaline granite, which result supports Bowen's theory of the interaction of basic magma and petlite.