In the area between the villages of Siquirres and Turrialba along the Rio Reventazon a number of teschenite sills outcrop which are associated with lavas of alkali basalt and basanite. The sills are up to 40 m thick and are emplaced in Tertiary marine sediments.
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Limon and Cartago
Along the northeastern side of the Cordillera de Talamanca, particularly on the Fila de Matama and in the Rio Chirripo, occur lavas of alkali basalt, basanite and nephelinite. The distribution is not known and no petrographic descriptions are available.