412 EECENT WOEK OF THE GEOLOGICAL SUKVET 



westwards. The folds were believed to have culminated in reversed 

 faults ; but it is now apparent that the latter need not necessarily 

 be preceded by folding. Secondly, in the horizontal section illus- 

 trating the previous report, the reversed faults in advance of the 

 great thrust on Ben Arnaboll are represented as extending down- 

 wards, till each pierced the buried platform of Archaean rocks. But 

 from the evidence obtained between Foinne Bheinn and Ullapool, it 

 is clear that such may not be the case. Numerous sections demon- 

 strate the fact that the strata, piled up by minor thrusts, have been 

 driven along a major thrust-plane, separating the underlying un- 

 disturbed masses from the overlying displaced materials. 



2. Classification of Terrestrial Movements. 



AVith the view of simplifying the description of the extreme 

 complications of this region, the following classification of the 

 various terrestrial movements is proposed. They may be arranged 

 in three groups, according to the magnitude and importance of the 

 displacements : — 



a. Minor thrusts or reversed faults. 



h. Major thrusts. 



c. Maximum thrusts. 



a. The reversed faults included in group {a) repeat the strata by 

 bringing lower to rest on higher beds, and lie at oblique angles to 

 the major thrust-planes. By means of them, the Silurian strata are 

 piled up to an enormous thickness. 



h. The major thrusts have driven the piled-up strata westwards, 

 along planes separating the displaced materials from the underlying 

 undisturbed strata. They always truncate the overlying minor 

 thrusts and may nearly coincide with the lines of bedding of the 

 strata over considerable distances. 



c. The maximum thrusts are by far the most powerful, because 

 they bring up and drive westwards portions of the old Archaean 

 platform with the Cambrian and Silurian strata resting on it, and 

 likewise usher in the eastern schists. The accompanying horizontal 

 section (fig. 8) shows the characteristic features of these various 

 displacements. 



3. Chief Maa^lmum Thrusts. 



There are several maximum thrusts throughout the area 

 affected by the movements, but three of them are of special im- 

 portance because they enter into the geological structure of the 

 complicated tract between Loch More and Ullapool. Stated in 

 order, passing from west to east, they are — 1, the Glencoul Thrust ; 

 2, the Ben-More Thrust ; 3, the Moine Thrust. The first is mag- 

 nificently displayed in dip section on Loch Glencoul and Loch 

 Glendhu, near Kylesku ; the second, on the great cliff of Ben More 

 in the Bealloch of Coinne-mheall ; the third, at Knockan near 

 Elphin and on the coast-section of the Moine between Loch Eriboll 

 and the Kyle of Tongue. 



