Quensel (1912, p. 79) has described a group of rocks he called 'essexites', together with 'comenditic granophyres' and syenites from the vicinity of Cerra Cagual. The essexites are gabbroic rocks with orthoclase but no nepheline. However, syenites contain aegirine-augite.
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Syenites comprising orthoclase, albite-oligoclase, aegirine- augite, arfvedsonite and a little quartz, and nordmarkites including quartz, fayalite and aegirine-augite are described from the Cerro Balmaceda vicinity by Quensel (1912, p. 36).
Extrusive rocks lying close to the north shore of Seno Skyring consist of labradorite, with some albite, pyroxene, altered nepheline, serpentine and magnetite in a glass base. Little detail of field relationships is available. Described as trachydolerite (shoshonite) by Quensel (1912, p.