334 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



The Carrig rock in the midst of Port-le- Murray Bay appears to 

 be a boss of the older limestone, of the same age as the patch of 

 limestone which is quarried at Port-le-Murray itself. How far in- 

 land the Poolvash limestones extend I have not as yet seen ; the 

 outcrop is seen at Knockrushen at the south-eastern side of the 

 basin, and they must have been denuded from the whole of Castle- 

 town Bay, if indeed they ever extended in that direction. 



On the whole then, it appears that we have evidence in proof of 

 the existence of some portion of the Isle of Man as an island about 

 the commencement of the newer Palaeozoic period, the Old red con- 

 glomerate forming a thin fringe, and occurring at the edge of the 

 southern basin as a mass of small white quartz pebbles in a car- 

 bonaceous paste not more than three or four feet thick. This thin 

 fringe does not appear however to have suffered denudation, but 

 passes regularly into the overlying dark-coloured limestones and 

 shales. It is worthy of notice that no granite boulders are found 

 in the Old red conglomerate; and the probable inference is, that 

 the granitic nucleus had not yet been brought to the surface. The 

 accumulation of beds reposing on the Old red indicate by their 

 fossils the presence of a fauna not unlike that of the lower Scar lime- 

 stone of Yorkshire. 



This early condition of the beds v/as soon affected by disturbances, 

 marks of several of which can be traced in the southern basin. 



And first, we find the lower beds contorted and partially broken 

 up, while volcanic ash, &:c. has become mixed with carbonaceous 

 matter, and passes into the black schistose Posidonian limestone, 

 this bed containing ferns, and forming the nearest approach to the 

 true coal-measures that the island affords. After this a second erup- 

 tion of volcanic matter took place ; and we may trace the formation 

 of a trap-breccia containing fragments of the Posidonia schist and 

 limestone and of the older trap-tuff. Lastly, there is evidence of at 

 least one disturbance posterior to this, in the intersection of the 

 entire area of the southern basin by a series of trap-dikes having a 

 general direction E.S.E. and W.N.W. 



The whole district under discussion exhibits what may be termed 

 an undulating structure, the ridges of the anticlinals running gene- 

 rally S.S.W. and N.N.E. : and it has been shown that the trap dikes 

 exhibit certain relations with these ridges, being compact and broad 

 on the ridges of the anticlinals, and branching out or ramifying in 

 the corresponding synclinals. The trap also does not seem to have 

 merely penetrated into old crevices ; but if we may judge from the 

 appearance of the bosses, must have forced itself in between the 

 schist and the tough beds of limestone, perhaps amongst the boul- 

 ders of the Old red conglomerate. 



There is, besides those already mentioned, a fourth system of 

 disturbances, wiiose direction is nearly N.E. by N. ; and these are 

 connected with the outburst of porphyries at a period later than 

 that of the deposition of the carboniferous strata. I have ventured 

 to conjecture that the date of this disturbance may be even more 

 recent than the deposit of the boulder clay. 



