Complex sentence: They are essentially of igneous origin, though some pyroxenites are included in the metamorphic complex of the Lewisian of Scotland; those pyroxene rocks which result from the contact alteration of impure limestones are described as pyroxene hornfelses (calc-silicate hornfelses).
Split into simpler sentences: They are essentially of igneous origin, though some pyroxenites are included in the metamorphic complex of the Lewisian of Scotland. The pyroxene-rich rocks which result from the contact metamorphism of impure limestones are described as pyroxene hornfelses (calc-silicate hornfelses).