OF THE SOUTH OF THE ISLE OF MAN. 435 



ill the qimdiant between N. and W. As they cut through all the 

 beds up to and including the Poolvash black marble and associated 

 tuff they must be newer than those beds, and Mr. Home * suggests 

 that they may be of Miocene age. The only evidence in favour of 

 their early Tertiary age is the fact that they agree with known Ter- 

 tiary basaltic rocks of the iS'orth of Ireland and the West of Scotland, 

 in being ophitic olivine-dolerites (or basalts) and in their prevalent 

 north-westerly strike t. They are quite distinct from the augite- 

 porphyrite scries aa Mr. Home points out ;j:, though Gumming was 

 inclined to regard them as accompaniments of it §. They usually 

 weather to a dark olive-green colour, and weathering generally takes 

 place more rapidly in their case than in that of the " country " rock, 

 giving rise to long channel-like depressions, which are often indi- 

 cated on the six-inch map. 



IV. Detailed Description of the Geology of Scarlet Point, &c. 



The numbers in the following description refer to the localities 

 marked on the map of Scarlet Point (PL XIV.). 



Starting at Castletown, let us follow the western shore of Castle- 

 town Bay southwards towards Scarlet Point. 



About 180 yards S.W. of the Scarlet limestone quarry we come 

 upon a small syncline in the limestone. Running along the bottom 

 of this syncline is a dyke [523] 5 feet wide ||. From 30 to 70 yards 

 south-west of this dyke we come upon a shingle-covered gap in the 

 limestone, 79 feet broad, in which the following occur : — 



Eeference 

 Feet. Number. 

 Branching olivine-dolerite dyke or dykes with 



inchided hmestone-patches 28 31 



Sliingle, &e. (see below) 13 



Black limestone... 5 



Augite-porphyrite dyke (?) 15 32 



Augite-porphyrite breccia 18 33 



Total 79 



"With regard to the 13 feet of " shingle, &c.," the south-western 

 7 feet are augite-porphyrite, perhaps not in situ ; but I believe the 

 greater part of the 13 feet to be occupied by the "melaphyre 

 dyke" [501] previously referred to (p. 434), for the following 

 reasons: — At a point 17 feet to the south of the "Spring" on 

 the map there is a small exposure of that dyke. The dyke can 

 be traced for 180 feet, and appears to occupy the line of a fault 

 by which the volcanic rocks have been thrown down on the south 



* Trans. Ed in. Geol. See. vol. ii. (1874) p. 336. 



t A. Geikie, ' History of Volcanic action during tbe Tertiary Period, &c.,' 

 Trans. Roy. Soc. Edin. 1888 (reprint), p. 30; but see also Judd, Quart. Journ. 

 Geol. Soc' vol. xlv. (1889) p. 209. 



+ Trans. Edin. Geol. Soc. vol. ii. (1874) p. 332. 



§ ' Isle of Man,' p. 244. 



II See Oumming's ' Isle of Man,* p. 122. 



