542 Mr. Archibald Geihe [June 7, 



Highlands, we encounter a totally different series of rocks. Though 

 greatly j^licated, dislocated, crushed, and metamorphosed, these rocks 

 can be recognised as unquestionably, in the main, of sedimentary 

 origin. They must be many thousands of feet in thickness, including 

 among their members such rocks as conglomerate, pebbly grit, 

 quartzite, black slate, audalusite slate, phyllite, mica-schist, fine 

 flagjzy gneiss, and limestone, together with intrusive sheets and bosses 

 of various eruptive rocks. Some of the groups of this series can 

 be followed and mapped for long distances with nearly as much ease 

 as the members of a succession of unaltered Pala30zoic or Secondary 

 formations. There is a belt of limestone, for example, which has 

 been traced by the Geological Survey almost continuously from the 

 coast of Banffshire to the west of Argyllshire, through the very heart 

 of the Highlands — a total distance of not much less than 200 miles. 

 These limestones have for the most part become so thoroughly crys- 

 talline that fossils can hardly be expected to be found in them, 

 though there are occasional less altered portions of rock which may 

 eventually prove to be fossiliferous. The limestones are associated 

 with quartzites and schists, as unaltered limestones are with sand- 

 stones and shales. I cannot myself doubt that they have been formed 

 by the aggregation of the remains of calcareous organisms. The 

 same rocks are prolonged into the north of Ireland, where one of the 

 dark limestones at Culdaff" has lately yielded certain bodies which 

 some palaeontologists have declared to be the remains of a coral 

 (Favosites). The black slates which so closely resemble the dark 

 carbonaceous shales of the Lower Silurian region of south Scotland 

 liave afforded in Donegal some curious pyritous markings strongly 

 suggestive of graptolites. 



Out of this enormous mass of metamorphosed sedimentary strata 

 the Scottish Highlands east of the Great Glen are built up, as well 

 as the region which extends southwards across the north-west of 

 Ireland as far as the centre of County Galway. The first question 

 that requires an answer with regard to it has reference to its relation 

 to the fossiliferous quartzites and limestones of the north-west. 

 Murchison, who led the way in the investigation of the stratigraphy 

 of the Highlands, believed that the quartzites and limestones of the 

 Central Highlands lay towards the base of the whole series of post- 

 Cambrian rocks, and were the south-eastward extensions of those of 

 Sutherland. But recent investigations throw some doubt on this 

 view, which at the time it was promulgated seemed so natural and 

 simple. We know that the quartzites and limestones of the Central 

 Hi<?hlands, so far from being near the bottom of the vast series of 

 schists, are underlain by many thousand feet of other metamorphosed 

 sedimentary strata, and that the actual base is nowhere reached in 

 that region. 



During the last two years, in concert with some of my colleagues 

 of the Geological Survey, I have devoted some time to the task of 

 endeavouring to find the bottom of these crystalline schists of Scot- 



