IN THE NORTH-WEST HIGHLANDS OF SCOTLAND. 41 1 



Loch Borrolan the limestone, as is well known, has been converted 

 into a beautiful white marble, which is found over a considerable 

 area. At Ledbeg the marbles underlie the intrusive sheet, and to 

 the east of Alltnacallagoch they are found resting on it in small 

 isolated patches. The marble is again traceable across the moor 

 southwards to Loch Urigill, while far to the north it is met with 

 on tho southern slope of Sgonnan More, immediately below the out- 

 crop of the Ben-More Thrust-plane to be afterwards referred to. Along 

 the eastern margin of the Loch-Borrolan sheet, it appears close by 

 the road leading to Loch Ailsh. The lithological characters of the 

 marble have been well described by Professor Heddle, who calls at- 

 tention to the presence of malacolite, serpentine, Wollastonite, 

 magnetite, and margarodite in the calcite-matrix. That the marble 

 is merely a portion of the limestone-series altered by contact with 

 the intrusive igneous rocks, as pointed out by Professor Heddle, can 

 be proved by most conclusive evidence. Passing outwards from the 

 margin of the intrusive mass, the observer can trace all the stages 

 of change from the crystalline to the unaltered bands of the cal- 

 careous series. Nay, further, it is possible to identify some of the 

 zones of the limestone even in the midst of the marble. In places, 

 however, the alteration has been so extreme that all traces of bed- 

 ding have been destroyed. Finally, sheets and dykes of granitoid 

 rocks occur in the marble, apart from the great Loch-Borrolan sheet. 



6. Sheets injected prior to Post-Lower-Silurian Movements. 



"While these igneous rocks have been intruded after the de- 

 position of the limestone, there is satisfactory evidence to prove that 

 the injections took place prior to the Post -Lower-Silurian movements. 

 Throughout the whole of the area affected by the displacements the 

 dykes and sheets are truncated by numerous reversed faults, like 

 the strata in which they occur. Further, they have in many 

 cases been made schistose by these displacements, and there can be 

 no doubt, therefore, that this phase of volcanic activity had ceased 

 before the great terrestrial movements began. 



Y. Physical Relations op the Strata between Eeieoll and 

 Ullapool. 



The conclusions to which the Geological Survey was led in the 

 district of Eriboll, regarding the nature and extent of the terrestrial 

 movements of Post-Lower-Silurian date, have been confirmed by the 

 examination of the line of complicated structure southwards to 

 TJllapool. 



1. Modification of two Inferences announced informer Official Report. 



There are two points, however, in the former official Eeport 

 which, in the light of recent evidence, require modification. First, 

 it was stated that during the incipient stages of the movements the 

 strata were thrown into folds, which became steeper along the 

 western fronts, till they were disrupted and the eastern limbs pushed 



