54 



PEOCEEDZN-GS OF THE GEOLOGICAL SOCIETY. 



referred to as the Logan* rock, is usually the Hebridean Gneiss? 

 which is often brought by an overthrow fault above different 

 members of the Assynt series. 



(4) The Eastern Gneiss, though actually overlying the Assynt 

 series in some localities, has been brought into this abnormal position 

 by earth-movements subsequent to the deposition of the latter, and 

 belongs to the Archaean group, but is nevertheless widely separated 

 in age from the Hebridean. 



In his earliest paper Dr. Callaway had been disposed to acquiesce 

 in the view which for a time found favour with several investigators, 

 myself among them, that the apparent sequence from the base of the 

 Torridon Sandstone to the Upper Gneiss might be a real one, 

 but that the fossiliferous limestone of Durness might not be 

 identical in age with the dolomitic limestone which appeared to 

 underlie the Upper Gneiss, hence that the rocks from the Torridon 

 Sandstone to the Upper Gneiss inclusive might all belong to 

 the Archaean series, though to a later part of it than the Hebri- 

 dean. This view Dr. Callaway, after more detailed work, was com- 

 pelled to abandon, and I am myself convinced that we must accept 

 the Torridon Sandstone, quartzite, and overlying limestone, whether 

 dolomitic or not, as deposits of Palaeozoic age. 



But the untenabilLty of the Murehisonian hypothesis had been 

 simultaneously demonstrated by yet another investigator. Professor 

 Lapworth, whose work in the southern uplands of Scotland had 

 rendered him especially familiar with disturbed districts, and with 

 the principles of mountain as opposed to lowland stratigraphy, 

 applied himself in the summer of 1882 to the study of the coast 

 region of Durness and ErriboU, selecting that as the one in which "a 

 demonstrably ascending succession from the basal Hebridean Gneiss 

 through fossiliferous Palaeozoic limestones into the metamorphic 

 gneiss and micaceous schist and slates f of the Central Highlands '" 

 was asserted to occur. The results of this work have been only in 

 part published, because, on revisiting the country in the summer of 

 1883, incessant labour and continuous exposure completed the ill 

 effects of a long period of excessive devotion to work, and brought 

 on most serioas illness, from which Professor Lapworth has hardly yet 

 comi^letely recovered. But you will remember that he exhibited in 

 this room a most elaborate map and sketch section, at the meeting 

 when Dr. Callaway's paper was read J, and showed how his detailed 

 work in the Erriboll region was in accordance with the main conclu- 

 sions at which that investigator had arrived. Professor Lapworth, 

 however, in the course of the jeai 1883 contributed three papers to the 

 Geological Magazine, entitled " The Secret of the Highlands."' These 

 papers, the first of which was published in the March number, I may 

 venture to assert will always hold a very high place among the contri- 

 butions to the elucidation of a problem which for so long has been the 

 special "crux " of British geologists. In the first. Professor Lapworth 



* Named from Glen Logan, near Loch Maree, also vn?itten Glen Laggan. 

 t The Upper Gneiss of Murchison and Geikie. 

 + May 9, 1883. 



