362 



C. CALLAWAY ON THE NEWEE GNEISSIC 



from Loch Broom. To these facts I have been able to discover no 

 exception in sections in which the rocks were undoubtedly unin- 

 verted. Throughout this paper I avoid the use of the terms " Lower " 

 and " Upper" in reference to the quartzite, in order to prevent any 

 confusion which might arise from the Murchisonian meaning of the 

 words. 



I have seen no reason to believe that the quartzite ever largely 

 exceeds 300 feet. The seemingly great thickening in certain loca- 

 lities is, in my opinion, due to repetition by folding or faulting. 



c 3 . Brown Flags (Fucoid beds).' — The rocks of this zone are very 

 varied. The predominant type is a fine-grained arenaceous flag, 

 which is sometimes argillaceous and sometimes dolomitic. There 

 are also soft, thin-bedded, argillaceous shales, dark slates, and thin 

 beds of dolomite and quartzite. The series, whatever its composi- 

 tion, is distinguished by the abundance of iron, which, by its per- 

 oxidation on weathered surfaces, gives rise to the characteristic 

 rusty-brown colour. 



I have found this band persistent from Loch Broom to near 

 Whitten Head. On Loch Broom the thickness is about 30 feet; 

 but in Assynt it has expanded to 100 feet, retaining about the same 

 thickness, or rather less, on Loch Emboli. In the last locality it 

 becomes more arenaceous, its upper beds passing into a kind of im- 

 perfect quartzite, in which siliceous seams, weathering out sharply 

 from vertical surfaces, alternate with softer material. This variety 

 graduates upwards into the next band. 



c 4 . Salterella-GW** and Quartzite. — This zone is distinguished by 

 the abundance of specimens of Salterella MaccullocJiii. On Loch 

 Emboli, where alone the fossils have been found, the beds are about 

 15 feet thick. Some of the strata are an iron-stained quartzose 

 grit ; but quartzite proper also occurs. The Salterella abounds in 

 both kinds of rock, but is in better preservation in the grit. In 

 Assynt 10 feet of quartzite holds a corresponding position between 

 the flags and the dolomite ; and on Loch Broom the quartzite has 

 considerably expanded, the flags being much thinner ; so that the 

 aggregate thickness of flags and Salterella-qu&rtzite is about the 

 same as in Assynt. 



c 5 . Dolomite. — Two years ago, before any doubt of the identity 

 of the Durness and Emboli limestones had been expressed, I was 

 struck with the fact that the latter was but slightly susceptible to 

 the action of hydrochloric acid ; so that I was quite prepared for Dr. 

 Heddle's announcement of their chemical difference. I have re- 

 cently applied the acid test to sixteen specimens, taken from widely 

 separated localities between Ullapool and Emboli. Eifteen of them 

 exhibit but very slight effervescence, except along joints, where de- 

 composition may be supposed to have supervened. The sixteenth, 

 from Loch Broom, where it was in contact with Hebridean gneiss, 

 effervesces more freely. But in this case chemical reactions have 



* Since this paper was written, an article has appeared in the ' Geological 

 Magazine,' by Prof. Lapworth, F.G-.S., in which the same name is proposed 

 for this zone. 



