Vol. 56.] EAKTH-MOVEMENT IN THE ISLE OF MAN. 15 



abut upon the above-mentioned pile of brecciated limestone ; and 

 at three or four places long narrow strips of the dark limestone 

 were found to shoot steeply upward and become most singularly 

 wedged in between the component blocks of the Volcanic Series, 

 while smaller shreds of similar limestone were completely isolated 

 among the coarse agglomerate which borders the Stack. In these 

 strips, indications of sliding and disturbance were everywhere 

 visible, and the outer surfaces were indurated into chert-like 

 material. It is difficult to give the evidence its full weight without 

 stating all the details, but I think that it can be proved that these 

 complexities have not been caused by the volcanic outburst, but 

 have been brought about at a later date by the differential 

 movement of segments of the eruptive rocks upon their original 

 floor of limestone. My interpretation of the phenomena is 

 embodied in fig. 1 (p. 14). 



V. The Section at Poolvash. (Fig. 2, p. 16.) 



At Poolvash the junction of the tuffs with the limestone may be 

 traced across the foreshore, in a direction slightly oblique to the 

 coast-line, for nearly § mile, presenting many variations in detail, 

 but everywhere exhibiting indications of relative displacement of 

 the overlying to the underlying strata. For the greater part of 

 this distance the ash rests upon the black argillaceous limestone- 

 flags (' Posidonomya-he&s ' of Gumming), which form the uppermost 

 member of the Limestone Series in the south of the island, but 

 near the western end of the outcrop, opposite Poolvash Farmstead, 

 it apparently comes at one place into juxtaposition with a somewhat 

 lower horizon (namely, the ' Poolvash Limestone ' of Cumming). 

 There is everywhere at the base of the ash a few inches of 

 crushed material possessing a platy structure, usually consisting of 

 decomposed ash, but sometimes of shattered black shale like that 

 intercalated with the limestone-flags. The surface of the limestone 

 beneath this plane is characterized by cherty induration and by 

 the presence of much pyrites, while bright slicken sides are occasion- 

 ally seen along fractures passing obliquely downward from the 

 junction. Sharp-cut planes of induration overlain by platy crushed 

 material are also present in the body of the ash above the junction. 



The most instructive section occurs on the south-eastern side of 

 the bay, under the remains of an ancient earthen fort, where the 

 limestone first emerges from beneath the tuff. At this point the 

 smooth limestone-flags have been rucked up into shallow folds 

 which, in a few feet, die out downward into gentle dome-like 

 undulations, but increase rapidly in steepness upward, and at the 

 junction break into sharp crests which shoot up into the ash almost like 

 intrusive dykes, and are then bent over towards the north, as shown 

 in fig. 2 (p. 16). These structures have been so admirably dissected 

 out by marine action that we may trace the limestone-anticlines 

 step by step along the foreshore in the direction of their axes (at 

 right angles to the figured section) ; and, as the folds have on the 



