1889.] on the Higldands of Scotland and the West of Ireland. 537 



oldest Arenig rocks, and may be equivalent to some part of the 

 "Primordial Silurian" or Cambrian series. This, however, is a 

 question that must remain unsettled until a thorough critical exami- 

 nation of the fossils has been completed. 



The area within which these Silurian quartzites and limestones 

 can be certainly recognised, forms a narrow belt extending for about 

 110 miles along the north-west coast of Scotland, from the northern 

 coast of Sutherland to the south of the island of Skye. Throughout 

 that extent of ground the rocks exhibit remarkable persistence in the 

 character and thickness of their several subdivisions, whence the 

 inference may legitimately be drawn that the area within which they 

 are now visible forms but a small part of the region over which they 

 were originally deposited. 



It was claimed by Murchison, and generally conceded by geologists, 

 that the quartzites and limestones of the north-w^est pass upward into 

 a younger series of schists, representing metamorphosed sedimentary 

 rocks. This order of succession appeared to be established by the 

 evidence of many clear natural sections along the whole tract from 

 Durness to Skye. It was first adopted and afterwards opposed by 

 Nicol, who in his later papers maintained that the supposed younger 

 schists were merely the old or Archaean gneiss brought up again by 

 great faults, and pushed over the younger formations. But he failed 

 to account for the striking difference in petrographical character 

 between the old gneiss and the younger schists, and for the remark- 

 able coincidence between the general dip of the latter and that of 

 the Silurian stratified rocks on which they seemed to rest conformably. 

 During the last ten years various geologists have renewed the investi- 

 gation of the question, among whom I may specially mention Dr. Hicks, 

 Professor Bouney, Dr. Callaw' ay, Professor Lapworth, and the members 

 of the Geological Survey, particularly Messrs. Peach, Home, and 

 Clough. The result of their labours has been, in the first place, the 

 discovery of one of the most complicated pieces of geological structure 

 at present known in any country ; in the second place, the abandon- 

 ment of all further controversy, and the attainment of complete 

 harmony regarding the order of geological succession in the north- 

 west Highlands. 



Murchison's view that there is a regular upward passage from the 

 quartzites and limestones into the upper schists is proved to be 

 erroneous, while Nicol's contention that the old gneiss is brought up 

 again above the Silurian rocks is found to be so far correct. But the 

 structure is now seen to be infinitely more com23lex than Nicol 

 imagined, while, on the other hand, Murchison's belief that the 

 younger schists were evidence of a gigantic metamorphism later than 

 Lower Silurian time is undoubtedly true, though in a sense very 

 different from that in which he looked at the question. 



Nowhere in the north-west Highlands can any rock be seen resting 

 in its original and natural position above the limestones. The highest 

 limestone of Durness is the youngest rock of that region about the 



