Pyroclastic cones resulting from Strom-bolian basaltic eruption are known as scoria cones, while eruptions of Surtseyan type produce tephra rings. These two types of cones have characteristic morphologic and lithologic features. Descriptions of tephra rings from the Valley of Mexico and considerations of the features of pyroclastic cones in general suggest that there is continuous variation between the distinctive morphologies of the two types of cone but that the lithologic characters of the pyroclastic material that forms scoria cones and tephra rings are distinctive and do not grade into each other.

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