372 ME. CLOrGH AND DE. POLLAED ON SPINEL [Aug. 1 899,. 



24. On Spinel and Foesteeite from the Glenelg Limestone 

 (Inveeness-shiee). By C. T. Clough, Esq., M.A., F.G.S., and' 

 W. PoLLAED, M.A., Ph.D., F.G.S. (Eead April 12th, 1899.) 



[Communicated by permission of the Director- Greneral of 

 H.M. Greological Survey.] 



The primary object of this commumcation is to describe the occur- 

 rence of two minerals — forsterite and true spinel — which are found 

 in close association in a limestone in Glenelg (Inverness-shire), but 

 which do not appear to have been recorded hitherto in Scotland. 

 Before tabulating the analyses, however, it may be well to mention 

 what has been previously written about the limestone, and to 

 describe to some extent its geological position and chief characters. 



The exposure from which the minerals were obtained is on the 

 southern side of the Big Glen, or Glenmore, of Glenelg, and it lies 

 at a distance of rather more than | mile east of the top of 

 Sgiath Bheinn (1-inch map 71, Inverness-shire 6-inch map 47). 

 The limestone-band to which the exposure belongs can be traced, 

 without any considerable interruption by faulting, for nearly a mile. 

 Its general direction is slightly east of north, and the width of 

 outcrop varies from a few yards up to 30 or 40. This lime- 

 stone is one of a group of limestones which have long been known, 

 and are noted for the variety of minerals that they contain. 



Macculloch, in his description of Tiree,^ states that ' sahlite, . 

 accompanied by tremolite and forming large nodules in Primary 

 limestone,' occurs in Tiree, Harris, and Glenelg, and that coccolite 

 and mica, in small crystals of a talcose aspect, are found in the 

 limestone in Tiree and Glenelg. In his 'IS^ew Geological Map of 

 Scotland,' bearing the date of 1832, the same author showed an 

 outcrop of limestone on the northern side of the Big Glen of 

 Glenelg. 



Murchison also speaks of the same limestone-group in his account 

 of the ' Succession of the Older Eocks in the Northernmost Counties 

 of Scotland.' ^ He says (p. 388), ' On the south side of Loch Duich . . . 

 some of the calcareous bands of highly crystalline limestone are 

 white, whilst others are chloritic and greenish and much resemble 

 the Connemara marble of Ireland, — such bands being finely inter 

 calated either in micaceous flagstones, in parts calcareous, or in finely 

 laminated slaty flagstones, which pass into a rock which must be 

 called gneiss.' In pi. xii, he publishes his ' First Sketch of a New 

 Geological Map of the North of Scotland,' and he shows a limestone- 

 band on each side of Loch Duich. 



It is, however, to the late Prof. Heddle that we owe most of our 

 knowledge of this limestone. In some of his ' Chapters on the 



1 ' Western Is. of Scotland,' vol. i (1819) pp. 53-56. 



2 Quart. Journ. Geol. Soc. vol. xv (1859) p. 353. 



