OF THK SOUTH OF TIIK ISLK OF MAN. 437 



to the iiortli of the dyke right up to the line of fault and melaphyre 

 dyke [501]. This agglomerate consists chiefly of more or less 

 rounded blocks of augitc-porphyrite three or four inches in diameter 

 (though larger blocks occur) embedded in a matrix of finer volcanic 

 tuff. Overlying this agglomerate to the north of the dyke [500 a] 

 ai'c several fragmentary patches of bedded augite-porphyrite lava, 

 e.[i. uos. 155 and 157. 



Within five feet to !N^. of the dyke [500 a] a mass of lava and agglo- 

 merate 63 feet long x 'liS feet broad (exposed) is tilted so as to dip at 

 45" to S. 19° W. Several other masses of augite-porphyrite occur, 

 of which it is often difficult to say whether they are to be regarded 

 as tilted lava-beds or intrusive dykes. 



At the spot marked 524 the geology is rather puzzling. The 

 agglomerate surrounding the dyke [500 a] abuts against a higher, 

 slightly overhanging, greenish mass, which appears under the micro- 

 scope to consist of very minutely amygdaloidal augite-porphyrite 

 fragments with a calcareous cement. Perhaps we have here a 

 faulted junction. To the west of 524 a deep cleft has been worn 

 by the sea, and a few yards west of the cleft lava is seen overlying 

 agglomerate and overlooking a second much longer, but shallower, 

 narrow inlet. It appears to me probable that a fault runs along 

 this inlet, for on the eastern side of it we have very distinct agglo- 

 merate, which does not appear to be present at all on the western 

 side. If there be a fault the downthrow is probably on the west, 

 for a bed of augite-porphyrite [171], 3 feet thick, on the western 

 side of the inlet, is tilted so as to dip at 22° to N. 71° W. 



Tuff overlies the bed of lava just mentioned, and extends for not 

 less than lOO yards westwards to a point where it is cut off by a 

 fault striking N. 53° W. The line of fault is excellently exposed, 

 the fine tuff devoid of blocks being brought into immediate contact 

 with a coarse agglomerate, both being bare of vegetation, so that 

 the boundary between them is as sharply defined as it is possible to 

 imagine. I believe the tuff to be on the downthrow side, although 

 on examining it towards the top of the exposure, near the margin 

 of the grass below the footpath, a few blocks of lava hardly as large 

 as a man's head may be seen, which may be an indication of the 

 coming on of the base of the agglomerate. The agglomerate forms 

 a strip bounded on the north-east by the fault just described and on 

 the south-west by another parallel fault, the evidence for which is 

 as follows : — A bed [174] of reddish-looking augite-porphyrite lava 

 1 5 feet thick, in places nearly vertical, in others dipping at 60° to 

 W. 53° S., rises like a wall to a height of 40 feet above the triangular 

 patch of agglomerate at its south-western base and can be traced 

 inland to the ruined shed 1 7 j'ards to S.W. of the " Remains of Burial 

 Ground " *. The present position of this lava-bed is evidently due to 

 a fault striking N. 53° W., as described (with section) by Mr. Home t- 

 The downthrow of the fault is on the south-west. On the north-east, 

 at a distance of 10 yards, a portion [525] of the same bed in its 



* See six-inch map, sheet !<>. 



t Trans. Edin. Geol. Soc. vol. ii. (1874) p. 334. 



