CUMMING ON THE ISLE OF MAN. 325 



clined to believe that the former intrusion of trap amongst the Old 

 red conglomerate exerted an upward pressure at various points. 

 It will be seen that both these series are in the immediate neigh- 

 bourhood of trap-dikes, the latter being included between two 

 dikes not more than thirty feet apart and parallel to one another, 

 while the former is actually' cut through by a dike which ramifies 

 just at the summit of the boss. The direct evidence however of 

 tabular masses of trap underlying altered limestone bosses has 

 only very lately been afforded me. It is exhibited just above low- 

 water mark on the shore betwixt the north end of Derby Haven 

 Pier and the little bay of Ronaldsway ; and it may be best seen 

 about fifty yards to the east of a limekiln formerly used near that 

 spot. And as we have an anticlinal axis or saddle running from this 

 very spot through the Skillicore bosses to the great fault at Coshna- 

 hawin, the chain of evidence appears to be complete as to the origin 

 of the bosses in question. 



I now proceed to describe seriatim those points of interest and 

 importance in the southern basin which may best lead to accurate 

 conclusions respecting its geological history. 



Starting from the south-western point of Langness, we find our- 

 selves upon the schists, whose general strike runs a few degrees north 

 of east (magnetic). A dike of greenstone is here seen at first running 

 along the northern edge of the ridge, and nearly in the same direction ; 

 and six yards further to the north there is a second dike parallel to 

 the former. The schist is contorted, and thrown into a synclinal 

 axis in the intermediate space. These greenstone dikes run into 

 the sea in a direction north-east by east ; and I believe that one of 

 them, or perhaps the two united, reappear on the top of the hill 200 

 yards to the north of the land-mark. At this point, at any rate, we 

 find a corresponding dike running into the sea on the south-eastern 

 side of Langness. The whole promontory of Langness is rent by 

 a series of chasms parallel to each other, and having a north-east 

 direction. A mass of greenstone is also seen, which seems to form 

 the nucleus or support of the ridge, and this is connected with the 

 first of these chasms, commencing at the extremity of the promon- 

 tory (see Map, PI. XV.). 



The second chasm exhibits a trap-dike running across the ridge, 

 and intersecting the former greenstone dike at an angle of 50°. I 

 consider this trap as newer than the greenstone ; and the difference 

 between them, both here and elsewhere, is easily traceable, the 

 former (greenstone) being of a lighter colour, extremely hard, not 

 so readily weathering, and prismatic in structure ; the trap, on the 

 other hand (corresponding with the Derbyshire toadstone), containing 

 a larger proportion of iron, easily weathering, often rotten, becoming 

 converted into clay exhibiting columnar structure, and ultimately 

 breaking up into spherical masses. The former would appear more 

 nearly allied to the granitic, and the latter to the basaltic family of 

 plutonic rocks ; and we may imagine the greenstone to have been 

 thrust up in a solid state, contorting the strata but not altering 

 them, and occasionally running so constantly along the line of strike 



