2i8 Mr. p. F. Kendall on 



In the Isle of Man many of the rocks which occur in the 

 Lancashire Glacial deposits are to be found, though in widely 

 different proportions ; thus, the Eskdale Granite, which is 

 so common on the mainland, is very rare in the Island, or 

 possibly absent, and the same is the case with the other Lake 

 District rocks, but their place is taken by Granites, Quartz- 

 porphyries, and other igneous rocks, which are clearly trace- 

 able to the great intrusive masses of Galloway. Intermingled 

 with these, to me, familiar rocks are many which were 

 entirely strange, and most prominent amongst them a fine- 

 grained granitic rock, which contained patches of a blue 

 mineral, presenting cleavages, which suggested to me that it 

 might be Riebeckite, the rare blue variety of Hornblende. 

 As this mineral was known in the British Isles only as a 

 constituent of a rock at Mynydd Mawr, in Carnarvonshire, 

 I submitted a specimen to Mr. Alfred Harker, of Cambridge, 

 who has described the Welsh rock, but he did not consider 

 that the Manx boulders could have been derived from the 

 Mynydd Mawr mass, as its structure and appearance were 

 different. 



In view of this opinion, I allowed the question to remain 

 undecided, until a new stimulus was given to my curiosity 

 by the discovery of a pebble of the same rock on Moel 

 Tryfan, Carnarvonshire, a hill about 2 miles distant from 

 Mynydd Mawr, From the occurrence of the rock in great 

 abundance in the Isle of Man, I was convinced that it 

 could not be of Welsh origin, and its absence from Lan- 

 cashire rendered it very improbable that it could be a 

 Galloway rock. 



I therefore sent a specimen to Professor Cole, of Dublin, 

 who confirmed my determination of the Riebeckite, but 

 could not recognise any similarity to any Irish rock. He 

 considered the rock of such interest as to be worthy of 

 description, and accordingly prepared some notes upon it 

 to be presented to the Mineralogical Society at their 



