Vol. 57»] SILFRIA]^ [?] ROCKS IN FORFARSHIRE, ETC. 339 



The Major Thrust. 



The junction of the Highland Rocks with the Jasper and Green- 

 Uock Series along the hillsides is more or less buried under Drift 

 and other materials throughout the whole of the largest patch of the 

 Silurian [?] rocks. But in the second, the evidence is fortunately 

 more satisfactory. Between the limestone-quarry last described and 

 the Bervie Water the course of the major thrust can, as a rule, 

 be accurately traced. That the slaty shale, the jaspers, and the 

 Green Rock are successively truncated by it as shown on the 1-inch 

 Geological Survey map, is especially clear ; for in several cases 

 these bands can be followed to within a few feet of the Highland 

 Grit, which can be traced persistently along the north side of the 

 thrust. 



In fig. 5 (p. 340) a reduced copy of a portion of the G-inch field- 

 map is given, in order to make this point perfectly clear: in no case 

 is any fault-rock seen. It becomes obvious, therefore, that this 

 major thrust is of great structural importance, and everywhere 

 separates the great mass of crystalline (Highland) rocks to the 

 north from the supposed Silurian rocks to the south, over which the 

 crystalline rocks have been driven. 



The Second Minor Thrust. 



The junction of the southern outcrop of the Margie Series in the 

 North Esk with the Jasper and Green-Rock Series is marked by a 

 zone of intense shearing, described on p. 329 as a wall-like mass 

 composed of leuticles. 



In view of the evidence already given, this line of junction must 

 also be a thrust-plane, for there is no ordinary fault-rock present, 

 and the phenomena are totally unlike those of ordinary faulting. 

 Though more important than the minor tihrust-plane already described 

 (see p. 337), it must also be a minor thrust, as it undoubtedly dis- 

 appears on reaching the major thrust. Unfortunately, the exact 

 place where the intersection takes place cannot be accurately fixed, 

 for the ground is covered with thick Drift, as already stated. 



V. The Position of the Major Thrust with reference to the 



Highland Rocks. 



As I have already stated (p. 335), in the area a little to the south- 

 west of that here described, the Old Red Conglomerate rests hori- 

 zontally upon the upturned edges of the sheared Margie Grits, and is 

 totally unaffected by the movements that produced the shearing. But 

 the conglomerate itself is in turn affected by the great Highland 

 Fault, which throws that rock down to the south in some cases for 

 several thousand feet. Now viewed on a fairly large scale, the 

 position of these two great movements, though of totally different 

 ages, is almost identical, and there must be some cause for this 

 approximate identity of position. This position we believe to be 

 fixed by the condition of the Highland rocks. It has been found that 



