On the Horizontal Movements of Rocks. 517 



160611% obtained by the Geological Survey from the Durness Lime- 

 stones confirms Salter's conclusions that they are distinctly of an 

 American type, the Sutherland quartzites and limestones being 

 represented by the Potsdam Sandstones and Calciferous Sand Group 

 of North America. 



After the deposition of the limestones, the Cambrian and Silurian 

 strata were pierced by igneous rocks, mainly in the form of sheets, 

 producing important alterations in the sedimentary deposits by con- 

 tact-metamorphism, the quartzites becoming crystalline, and the 

 limestones being converted into marble. 



"When this outburst of volcanic activity had ceased, terrestrial dis- 

 placements ensued on a stupendous scale. By means of powerful 

 thrusts the Silurian strata were piled on each other, and huge 

 slices of the old Archaean platform, with the Cambrian and Silurian 

 strata resting on it, were driven westwards for miles. With the 

 view of illustrating the extraordinary complications produced by 

 these movements, a series of horizontal sections was described drawn 

 across the line between Eriboll and Ullapool. 



The evidence relating to regional metamorphism was next referred 

 to, from which it is obvious that with each successive maximum 

 thrust there is a progressive amount of alteration in the displaced 

 masses, as the observer passes eastwards to the higher thrust-planes. 

 Eventually the Archaean gneiss is so deformed that the Pre-Cam- 

 brian foliation disappears and is replaced by new divisional planes ; 

 the Cambrian grits and shales are converted into schists ; the Silu- 

 rian quartzites into quartz-schists ; the limestones become crystal- 

 line ; the sheets of intrusive felsite, diorite, and granitoid rock pass 

 into sericite schist, hornblende-schist, and augen-gneiss respectively. 



These researches furnish a vast amount of evidence in support of 

 the theory that regional metamorphism is due to the dynamical and 

 chemical effects of mechanical movement acting on crystalline and 

 clastic rocks. It is also clear that regional metamorphism need not 

 be confined to any particular geological period, because in the jST.W. 

 Highlands, both in Pre-Cambrian time and after the deposition of 

 the Durness Limestone (Lower Silurian), crystalline schists and 

 gneiss were produced on a magnificent scale. 



2. " On the Horizontal Movements of Eocks, and the relation of 

 these movements to the formation of Dykes and Faults and to Denu- 

 dation and the thickening of Strata." By William Barlow, Esq., 

 E.G.S. 



The paper commenced with a description of some horizontal move- 

 ments of rocks caused by gravitation ; and the author quoted Mr. C. 

 E. Dutton's descriptions of the Grand Canon District, especially noting 

 the fact that between succeeding escarpments the strata dip slightly 

 from the crest of the one below to tbe foot of the next above, and 

 that whilst the strata of the median parts of each terrace are nearly 

 horizontal, the inclination increases as we approach the escarpment 

 of the next higher terrace, and also that Dutton observed indications 



Phil. Mag. S. 5. Vol. 25. No. 157. June 1868. 2 M 



