G. W. Tyrrell — Petrology of Arran. 307 



orthopliyre of the Eildon Hills, Melrose. The latter differs only in 

 its somewhat coarser grain, and in the abundance and large size of 

 its areas of riebeckite. ' 



2. Ckinanites op "WsiTiifG Bay and Dippin. — The crinanites 

 are ophitic olivine-analcite-dolerites occurring as dykes in many 

 parts of Argyllshire and the Western Isles. They are so called from 

 Loch Crinan, which lies almost in the centre of their area of 

 distribution.^ They are closely associated with olivine-dolerites 

 which differ from them only in the absence of analcite, and also with 

 the remarkable monchiquites and camptonites which have recently 

 been described from Colonsay and Mull. Complete descriptions of 

 this suite of dykes have been given by Dr. J. S. Flett in recent 

 Survey memoirs, and chemical analyses have been made in the 

 Survey laboratory.^ 



These dykes have the north-west trend so common in the Tertiary 

 suite of the Western Isles and the adjacent mainland. Their 

 unusual petrological character, however, has rendered their connexion 

 with Tertiary igneous activity of some dubiety. In the south 

 of Mull a few undoubted Tertiary dykes of analcite-dolerite have 

 been found, and Mr. Wright has found analcite-dolerites amongst 

 the north-west dykes of the Beinn Dearg group in Skye.^ 



The crinanites show transitions to the camptonites in their type- 

 locality, and also have many resemblances to the Carboniferous 

 teschenites which are common in the Midland Yalley of Scotland. 

 Dr. Flett, however, enumerates four differences : they are finer in 

 grain than the teschenites, have a perfect ophitic texture, hornblende 

 and biotite are scarce, and they occur as thin, vertical, parallel dykes 

 instead of sills.* One might add that in general they are much 

 richer in olivine than the teschenites, but poorer in analcite and 

 alkali -felspars. These mineralogical differences are clearly brought 

 out in a comparison of the chemical analyses of the two rocks. The 

 teschenites are much richer in alkalies and combined water, but 

 considerably poorer in ferrous iron and magnesia.* 



The present paper records the occurrence of a dyke of crinanite at 

 Whiting Bay in the south-east of Arran, and also records that the 

 great sill of Dippin, hitherto regarded as a teschenite, is much closer 

 in its affinities to crinanite. The sills of Kingscross and of the 

 Clauchland Hills are also to be regarded as crinanites. All these 

 rocks intrude the Triassic sediments, and are most probably of 

 Tertiary age. The Arran occurrences thus furnish one more link in 

 the chain of evidence which connects the crinanites and the associated 

 monchiquites and camptonites of the type-locality of Argyllshire 

 with Tertiary igneous activity. 



1 Summ. Prog. Geol. Surv. for 1909, 1910, p. 52. 



- The Geology of Knapdale, Jura, and North Kintyre, 1911, pp. 116-18 ; 

 The Geology of Colonsay and Oronsay, with Part of the Boss of Mull (Mem. 

 Geol. Surv.), 1911, pp: 41-6. 



^ The Geology of Colonsay and Oronsay, 1911, p. 41. 



* The Geology of Knapdale, Jura, and North Kintyre, 1911, p. 117. 



* For analyses of teschenites see The Geology of the Neighbourhood of 

 Edinhurgh (Mem. Geol. Surv.), 1910, p. 299. 



