8 THE JOURNAL OF GEOLOGY. 



Cambrian (possibly in part Lower Silurian) strata can be 

 traced, the lower portion consisting of quartzites, the central 

 and upper parts of various limestones, sometimes abundantly 

 fossiliferous. Nowhere else in the north of Scotland can so 

 thick a mass of early Palseozoic rocks be seen. Elsewhere the 

 limestones have been in large measure replaced by a complex 

 group of schistose rocks which rest upon the Cambrian strata, 

 and like them dip, generally at gentle angles, towards the east. 

 It was the opinion of Murchison, and was commonly admitted 

 by geologists, that these overlying schists represented a thick 

 group of sediments, which, originally deposited continuously 

 after the limestones, had been subsequently altered into their 

 present condition by regional metamorphism. They were vari- 

 ously named the " Eastern schists," the " younger gneiss," the 

 " gneissose and quartzose flagstones." Nicol, who at first 

 shared the general opinion regarding them, afterwards main- 

 tained that they did not belong to a later formation than the 

 limestones, but were really only the old gneiss, brought up again 

 from beneath by enormous dislocations and over-thrusts. We 

 now know from the labors of Professor Lapworth and the officers 

 of the Geological Survey, that Murchison and Nicol had each 

 seized on an essential part of the problem, but that both of 

 them had missed the true solution. Murchison was in error in 

 regarding his younger gneiss as a continuous sequence of 

 altered sedimentary rocks conformably resting on the Cambrian 

 (or to use his terminology, Lower -Silurian) formations. But 

 he sagaciously observed the coincidence of dip and strike 

 between the schists and sedimentary rocks below them and 

 inferred that this coincidence, traceable for many leagues, 

 proved that the metamorphism which had given these schists 

 their structure must have taken place after the deposition of the 

 Durness limestones. Nicol, on the other hand, with great insight 

 recognized that there was no continuous sequence above those 

 limestones, but that masses of the old gneiss had been thrust 

 over them by gigantic faults. But he failed to see that no mere 

 faults would account for the coincidence between the structural 



