The members of both the French and the Italian Commissions agree in ascribing the peculiar form and relative positions of the isoseismal lines to geological conditions. To the east of the epicentre, the schists and crystalline limestones form a deep, uniform, and compact mass; while, to the west, the old crystalline rocks are covered by jurassic, cretaceous, and eocene formations, constituting a less homogeneous and less elastic mass, in which the intensity of the shock would fade off much more rapidly, with the result that the epicentre occupies the western focus of the elliptical boundary of the meizoseismal area (Fig. 19).[35] That mountain-ranges have an important influence on the form of isoseismal lines is evident from both maps (Figs. 19 and 20), but especially from that published by the French Commission (Fig. 20). The resistance offered by the Sierra Nevada to the propagation of the earth-waves is shown in the former map by the approximation of the first and second isoseismals at the east end, and in the latter by the great bay in the third isoseismal line. Whichever interpretation of the evidence is the more accurate, the action of the mountainous mass is clearly to lessen rapidly the intensity of the shock--an effect which is probably due to the abrupt changes in the direction and nature of the strata encountered normally by the earth-waves. On the opposite side of the epicentre, the waves meet the Sierra de Ronda obliquely. In traversing this range, the shock lost a great part of its strength, while it continued to be felt severely along its eastern foot, thus giving rise to the south-westerly extension of the third isoseismal in Fig. 20, and, though to a less extent, that of the second in Fig. 19. _Fissures, Landslips, etc._--The earthquake resulted in many superficial changes, such as fissures, landslips, and derangement of the underground water-system--all changes of the same order as the destruction of buildings--but, so far as known, in no fault-scarps or other external evidence of deep-seated movements.