The area divides into the Haliburton-Hastings Highland complex of gneisses in the northwest and the Hastings basin of lower grade sedimentary rocks, principally limestones and pelitic schists and gneisses, in the southeast. The structure is dominated by the Cheddar granite batholith in the southeast, the Cardiff plutonic complex of granitic and syenitic sills and metasedimentary gneisses in north Cardiff Township, and the Faraday granite sheet in north Faraday Township. In Cardiff Township nepheline syenites occur in a southward-dipping syenitized zone of mixed gneisses flanking the southward-dipping Faraday granite sheet. The nepheline-bearing rocks are gneissic and are variable in mineralogy both across and along the strike. They are conformable with the associated metasediments and syenitic gneisses, but they also intrude and replace metasediments and metagabbros and are themselves intruded and replaced by alkaline syenite. The nepheline gneisses consist essentially of nepheline and albite or oligoclase, with microcline and microcline perthite sometimes present. Biotite, hastingsite, aegirine and magnetite are important mafics in some varieties; garnet, scapolite and corundum are characteristic accessories, with minor accessories including idocrase, muscovite, sphene, tourmaline, apatite, zircon, sodalite, cancrinite, fluorite, calcite and zeolites. At the Bentley-Siddon Lakes area in Faraday Township, the Faraday gabbro is cut by ijolite and nordmarkite and altered to garnet- hastingsite-hedenbergite-sodic plagioclase plus or minus scapolite and nepheline assemblages with corona textures in a rock which has been termed an "alkaline skarn" (Mitchell, S.L., 1976). Mylonitized nepheline syenite gneisses occur in Faraday Township (Hewitt, 1959, p. 29 and 1961, pp. 58-63). It has been suggested that fluorite-calcite-apatite veins that flank the Cardiff plutonc complex may be carbonatitic.