Bien que la majorité des roches soit d'origine volcanique avec des diaclases produites par le refroidissement des laves après leur emplacement, il y a raison de supposer que beaucoup d'affleurements ne montrent pas des effets thermiques, mais surtout des effets tectoniques.
Although the rocks on these islands are mostly of volcanic origin, evidence is adduced that many joints can be considered as of tectonic origin and that those not of tectonic origin, viz. those caused by shrinking of lava during cooling, can be expected to cancel out in a statistical evaluation procedure due to their random orientations.springer springer