19 



rocks was to retain the name Cambrian from North Wales, and the 

 highest that of Silurian from South Wales, it would be appropriate 

 that the middle division should be named Ordovician from *" the 

 last and most valiant of the old Cambrian tribes," whose geo- 

 graphical location was midway between the two areas, t" Every 

 geologist will at last be driven to the same conclusion that Nature 

 has distributed our lower Palaeozoic rocks in three sub-equal 

 systems, and that history, circumstance, and geologic convenience 

 have so arranged matters that the title here proposed for the central 

 system is the only one possible." It is quite needless to point out 

 how completely this forecast has been verified. 



C. THE NORTH-WEST HIGHLANDS OF SCOTLAND. 



For many years, as the science of petrology had been growing, 

 doubt had been felt as to the correctness of conclusions founded 

 on the apparent succession made out by Murchison in the North- 

 West Highlands of Scotland. Here four great Systems of rocks 

 Lewisian (Laurentian) , Cambrian (Torridonian) , Lower Silurian 

 (Assynt), and Higher Silurian (Eastern Gneiss) were supposed to 

 succeed one another in stratigraphical sequence, broken by two 

 unconformities. The logical result of this reading of the succession 

 was inevitably met by the grave difficulty that while the lowest 

 and highest members of the sequence are crystalline gneisses and 

 schists, the two middle members are at the most only very slightly 

 metamorphosed, and indeed are generally ordinary sedimentary 

 rocks still retaining clastic structures and well preserved fossils. 

 Alternative explanations applicable to parts of the sections had 

 been proposed by Nicol, Hicks, Callaway, Bonney, and Hudleston ; 

 but there was no comprehensive refutation of the basic error. 

 Lapworth's experience of the mountain structures of the Uplands, 

 with their deceptive appearance of normal sequence, suggested the 

 possibility that here, too, the apparent simplicity might be a mere 

 mask of intense complexity, and that rocks which had undergone 

 so much chemical change were not likely to have escaped the 

 violent earth movements which had produced such effects in the 

 Southern Uplands. This presented a new problem really worthy 

 of attack on account of the vital principles involved, and in 1882 

 Lapworth began his Highland work. 



THE SECRET OF THE HIGHLANDS (30). 



His method of attack was precisely that which had already 

 led him to success. He saw that if his southern method we're to 

 be pursued the clue to the structure of the region would be found 

 by him in the two middle series of sediments rather than in the 

 complicated crystalline rocks. 



* 17. P- M- I 17. P. 15- 



