ANNIVERSARY ADDRT^.SS OF THE PRESIDENT. 73 



the equivalents of those of Durness. This identification may yet be 

 shown to be correct, but must be regarded as still unproved. Traces 

 of fossils (annelid-pipes) liavo been found in some of the quartzites, 

 but thoy afford little or no help in determining the horizons of the 

 rocks. In Donegal, where similar quartzites, limestones, and schists 

 are well developed, obscure indications of organic remains (corals and 

 graptolites) have likewise been detected, but they also fail to supply 

 any satisfactory basis for stratigraphical comparison. I have myself 

 no doubt that the rocks arc far more ancient than any that could be 

 classed as Lower Silurian, though it is of course conceivable that 

 portions of even Lower-Silurian strata have been caught in their 

 plications and have undergone metamorphism. If they are claimed 

 as pre-Cambrian, I am not aware of any better proof that can be 

 furnished against than in favour of such a claim. They may 

 possibly include equivalents of the Torridon sandstone as well 

 as the Durness groups, and even portions of the upthrust Archaean 

 platform. 



This scries of schists consists mainly of altered sedimentary rocks. 

 Besides the quartzites and limestones there occur thick masses of 

 clay-slate and other slates and schists, with bands of graphitic 

 schist, greywacke, pebbly grit, boulder-beds, and conglomerates. 

 Among rocks that have been so disturbed and foliated it is necessarily 

 difficult to be always sure of the true order of succession. In the 

 Central Highlands, however, a certain definite sequence has been 

 found to continue as far as the ground has yet been mapped. Were 

 the rocks always severely contorted, broken, and placed at high 

 angles, this sequence might be deceptive and leave still uncertain 

 the original order of deposition of the whole series. But over many 

 square miles the angles of inclination are low, and the successive bands 

 may be traced from hill to hill, across strath and glen, forming escarp- 

 ments along the slopes and outliers on the summits, precisely as 

 gently undulating beds of sandstone and limestone may be seen to do 

 in the dales of Yorkshire. It is difficult to resist the belief, though 

 it would be premature to conclude, that this obvious and persistent 

 order of succession really marks the original sequence of deposition. 

 In Donegal also a definite arrangement of the rock-groups has been 

 ascertained which, when followed across the country, gives the key 

 to its geological structure*. 



The following table shows, in the apparent descending order, the 



* Geol. Survey Memoirs: Geology of N.W. Donegal, 1891. 



/2 



