W. C Simmons — Granite of Fuxdale, Isle of Man. 351 



sequence of crystallization quartz is the final mineral to consolidate. 

 "We have seen from the quarry sections that the thick veins of quartz 

 are not so regular as first supposed, and are usually inclined at angles 

 with the vertical. It should be noticed also that sometimes the 

 granite is veined and stringed with small quartz veins from \ to 

 3 or 4 inches in width. This is a local phase and occurs a little 

 to the west of the summit of the hill. The evidence seems to warrant 

 the idea that the veins of quartz represent the final consolidation 

 product of the granite magma. If this is the case cooling must indeed 

 have been slow to allow them to crystallize on such a large scale. 

 The selvages found to some of the veins support this theory also. 

 In one case there is a layer half an inch thick of mica in every way 

 similar to the mica of the granite and of the pegmatite. In another 

 case a lining of quartz and orthoclase felspar occurs as above described. 

 It would seem that these linings are due to the mass of the molten 

 silica with impurities being subjected to a process of segregation, 

 the magma being mobile and the cooling so slow as to allow in the one 

 case the mica and in the other the felspar to be separated and gathered 

 together at the sides, and after an interval the silica to crystallize 

 slowly. All the veins at present seen in the Foxdale Quarry show 

 a very coarse structure, but, as stated, in the Eairy Quarry finer- 

 grained quartz veins occur with also pegmatite. The quartz veins 

 outside the granite are usually rather fine-grained. 



At the point marked 'Aplite ' on the Map (Plate XVI) a quartz rock 

 of doubtful nature occurs. It resembles a dyke in its field relations, 

 but the exposure is not good. It is associated with sheets 3 inches 

 thick running in the slates parallel to the bedding, and though at first 

 taken for a dyke it more probably is an altered grit faulted off on one 

 side. In section it most resembles an impure quartzite. 



There is a decided break between the consolidation of the plagioclase 

 and the quartz, and the former occurs always in well-lamellated 

 idiomorphic crystals. In a section of the granite from the Foxdale 

 Silica Quarry all three felspars are present, and all the felspars as well 

 as the muscovite include small fragments of quartz. The microcline 

 is always interstitial. Garnet occurs in small irregular grains locally. 

 Apatite is present, but not common. The rock is a soda granite with 

 a rather high silica percentage. A good approximate analysis is as 

 follows : — 



Si0 3 72-5 



A1 2 3 16-3 



FeO ( lb 



MnO — 



CaO 1-1 



MgO 0-5 



K 2 3-2 



Na 2 3-2 



Ti~0 2 0-2 



P2 3 trace 



CI ....... trace 



H2O % . . 0-54 



100-04 



