CUMMING ON THE ISLE OF MAN. 339 



the west side of Castletown Bay, under the lime-kilns. The lime- 

 stone rising there on a steep inclination is most distinctly grooved 

 and scratched in parallel lines, the direction being magnetic east and 

 west*. We have similar groovings, and with the same bearings, on 

 the surface of the Posidonia schist, in the east of Poolvash Bay, near 

 the marble quarry -|-. Now had the drifting current come from the 

 W.S.W., it would almost necessarily have carried along with it, in 

 passing over Scarlet Head, some of the trap-tuff and fragments of 

 the Posidonia schist ; but at the before-mentioned locality near the 

 Stack, where the scratchings and the boulder clay are well seen, and 

 which is only a few hundred feet to the eastward of the trap-tuff j I 

 have not yet found a single fragment of this rock, though there occur 

 in it pebbles of the Old red conglomerate, and some of the foreign 

 rocks to which we have already assigned a Lower Silurian origin. 

 The same conviction as to the direction of the drift arises from an 

 examination of the colour of the boulder clay where it is in contact 

 with the subjacent rock. In Poolvash Bay, to the westward of the 

 trap-tuff, it is of a yellowish brown colour, and very ochreous. Near 

 the Stack of Scarlet it is dark blue, having obtained its materials 

 from the dark limestones and shales of Castletown Bay. Further to 

 the eastward we find it on the Brough, of a reddish brown tinge, 

 which it seems to have derived from the beating of denuding waves 

 upon the escarpment of the Old red conglomerate above Coshna- 

 hawin Head. At Port-le-Murray again, near the lime-kilns, it is of 

 a dingy dark blue colour, possibly obtained from the older dark lime- 

 stones and shales of Poolvash Bay. 



The best development of the boulder formation inland is in the 

 valley westward of the Creggins, where it is laid bare by the con- 

 tinued erosion of the Castletown river. The difficulty before men- 

 tioned, of distinguishing the more gravelly portions of the boulder 

 clay from the drift, renders it uncertain whether the rounded hill 

 above Rushen Abbey J, to the north-east of Ballahot (11.5 feet above 

 the level of the sea), should be considered as belonging to the for- 

 mer deposit ; but it appears in every respect similar to the Brough, 

 and, like it, rests upon a sudden elevation of the Old red conglomerate. 

 There has probably been large denudation of tlie more sandy upper 

 portions of this deposit, which has been partly re-arranged in the lower 

 level of the southern basin. It is not clearly exhibited in any emi- 

 nence westward of Malew Church ; but as there is some appearance 

 of it on the banks of the stream near Colby, and it is distinct along 

 the sea-shore to tlie south of Kentraugli and Mount Gawne, and so 

 round to Port-le-Murray, we may safely regard it as forming, either 

 in its original or re-arranged condition, the substratum next above 

 the older locks in most parts of this Ijasin ; it appears also to form 



* It is perhaps well to ol)servc that this direction is not the dip of the subjacent 

 scratched limestone, wliieh is more to the south, though varying. 



t Tlie limestone at Perwiek IJay is scratched and grooved with nearly the same 

 bearings, but directed rather more to the south, as we should expect, tlie current 

 being turned in that direction by tlie coast. See Map of the Island, I'lute XIV. 



X All the hills in this neighbourhood have greatly the character of the Scandi- 

 navian trainees or osar, the longer {txis running from N.E. by E. 



